Well, I confess I still wonder whether the choices I made in my first play through the game were really the best I could take, or the ones most appropriated for my character. As usual, lots of people raise plenty of good points in favor of choices I didn't take and against the ones I took, which usually just gets me more anxious to see how these choices will turn out in the following games.

At any rate, I will try to point out the reasons why I took the choices I did with my character, not intending so much to defend them as the best ones as to clarify why I did take them.
At first, I was considering marrying Anora with Alistair, if he somehow acquiesced to it. But, idealistic as my character was, in a manner of speaking, he wasn't willing to force Alistair into the throne, if there was another viable choice (and not just an alternative that would screw everything up), so as he started to figure out that Eamon's concerns about Queen Anora being elected queen weren't really legitimate concerns, but rather focused on nearly superstitious beliefs about Alistair's "bloodline" and nobility in general, and after he realized there was no way (not-hardened) Alistair would accept being king (he could
do it, but that's not quite the same as
accepting it, since it would never be what he truly wanted to be and to do), even less so while marrying with Anora, he decided to support her. In fact, one of my character's greatest disappointments was to see whom he considered his best friend, and whom he believed to be capable of accepting whatever it took to do the right thing, reacting so childish and cowardly to the prospect of being king. He thought Alistair was stronger than that.
But the worst, really, was at the Landsmeet, after my character defeated Loghain in the duel. Again, since he's idealistic in a manner of speaking, he saw no point in killing Loghain, since he didn't seem to be any more of an immediate threat, could do so much more good alive and did not seem to fake his willingness to start anew. Of course, though, that's when Alistair throws a hissy fit and starts to say things that seemed outrageous and unbelievable for my character, coming out from Alistair's mouth - the worst of them being when he said that if it was what it took to kill Loghain, he'd be king. At this point, there's alot going on: If Alistair becomes king alone, he kills Loghain, and, most likely, doesn't handle the role of king with the maturity that would be required to do it. If Anora becomes queen, Alistair leaves to never return, and one valuable and worthy, even if undoubtfully imature Grey Warden, not to mention my Warden's best friend, leaves forever and suffers a lot with his own condition. So my Warden tries one last time to suggest that Anora and Alistair could marry... In vain, obviously. But, in that case, he simply couldn't give Alistair the throne, after all of what just happened. If he did, he would be condoning Alistair's petty vengeance and allowing him to do it, killing needlessly (in his opinion) a man for the sake of his veangeance. He couldn't allow Loghain, or any man, to be killed on such petty basis - even less so by the man which was supposed to become the king. Behavior is crucial, and condoning such an act of vengeance would be condoning its correlated behavior, and, even worse, condoning that a king figure behaves in such a way - which would necessarily affect the way Ferelden was ruled, because it would have to do with the way its king behaved. In a nutshell, he couldn't let a man be killed just for the sake of vengeance, and he couldn't give Ferelden to what seemed to be unstable and imature hands. On the other hand, there had been given already plenty of reasons why Anora would be an excellent ruller, and even though she did seem to behave sometimes a little too pragmatically (like her father, in a way), she did seem a much better choice to Ferelden, and no one had to get needlessly killed in order to put her on the throne. So, in the end, my character put her in the throne, which got him the minor disappointment of seeing Anora order Alistair's execution - which just corroborated how overly-pragmatic she could be at times. Of course, my Warden didn't allow it, and Alistair left forever... Not the happiest of the resolutions, but he had a hard time picturing himself doing it differently. It just seemed inacceptable to condone a behavior such as Alistair's, even less so making one that behaves as such king of Ferelden.
As for the Dark Ritual, it was a really hard decision for my character... He really loved Morrigan, and he did believe her intentions were good up to some point (he did believe she was trying to save him too), and beyond that point, weren't evil. But there seemed to be something about doing this ritual that went beyond the scope of her intentions... A kind of magic that had everything to get out of control and have nasty consequences. And this wasn't some kind of Chantry fanatism on how blood magic is evil and and blood mages are therefore evil as well. Even as a mage raised in the Tower, my mage had absolutely nothing against apostates and found it outrageous that they were blindly hunted by the Chantry (case in point, he had a relationship with Morrigan and would later on become really close friends with Anders). And he didn't believe mages who dabbled in or used Blood Magic were automatically evil (again, case in point, Morrigan, or even Jowan). But he did believe that there was something inherently... wrong about Blood Magic, and inherently dangerous. Because blood magic always involved, by principle, forcing control over some another being or using in a too invasive manner one's life source - therefore being always wrong in at least one fundamental way. Not only that, this kind of magic seemed to him to always stimulated actions and behavior which could eventually, as these actions piled on and these behaviors got further rooted in the person, lead someone astray or have direful consequences, at the very least. So that was one reason to not believing that the DR would end up well. But there was also plenty of others: who was to say what this Old God would be like? He did believe when Morrigan said he wouldn't carry the taint of the evil that once took him, but that didn't mean that he couldn't be evil, or at least dangerous, for any other number of reasons. This was an Old God we were talking about: how could she be sure that he would behave the way she expected him to or desired him to? What could it mean, more precisely, that he would be an "avatar" of Freedom? Did it mean that no one would be able to stop him from being free? Or did it mean that he could do whatever he wanted to anyone, no matter what the consequences were for them? And just how easily could the first type of freedom become the second or even be intrinsically related to it? What's to stop an irrestricted force to become a tyrannic force? Wasn't that, after all, precisely what the Old Gods had become before, with the Tevinter Empire? (Not entirely sure on this one: nevertheless, the Old Gods became, with the darkspawn at least, the very embodiment of this tyrannic force) What's to say history wouldn't repeat itself, then? Not to mention just the questions about how the OGB would fit up to that moment to Flemeth's plans, which there was no way to tell whether they would be good or bad for Ferelden, but seemed to involve a lot of danger, considering how Flemeth didn't seem to really care about anyone's well being other than her own, even when she saves you at Ostagar. Morrigan seemed simply too over-confident on her ability to handle the OGB, and my Warden couldn't be just as confident as her. So, finally - it was, after all, a really hard decision - he decided not to do it. Whatever they had to defeat now would be definetely defeated, and there would be no chance of it becoming an unfinished business.
Of course, that meant my Warden not only lost his best friend, but also the woman he loved. He obviously didn't want any of that... But he wasn't willing to give up on his principles and make his decisions based on what he wanted, instead of doing it based on what he thought and felt was right.
Finally, when it came to the AD, he let Loghain do it. It might've been a coward decision... But if he did think that it was best for Loghain to be alive instead of him, he would've done it instead. But truth is, he was worried about what could be the long-term consequences of Loghain's survival, worried that he might again, for the sake of Ferelden, go astray and do yet another terrible and irreversible mistakes. While he was sure Loghain admitted his mistakes, he didn't feel as if Loghain had changed so much that he wouldn't do something a like again. And he felt like there had to be someone around precisely to fight and try to avoid this kind of mistake, mistake's based on far too extremists outlooks - someone had to fight to not let things be taken too far.
Nevertheless, he wouldn't ever force Loghain into doing it, not even suggest him to - perhaps he wouldn't even allow Loghain to do it if he felt he was doing it reluctantly, if he felt he was not at ease choosing to do it. But Loghain seemed earnest on his willingness to do it, not having any expectations that someone else should do it instead. He seemed completely satisfied with his decision. And it was also a very meaningful decision: one that would allow him to "repent" for what he had done, to do something for the actual good of Ferelden, something undoubtedly so - and there was obviously nothing else he would want more, even his own life. There was definetely nothing he would consider a better way to go than sacrificing himself in order to save Ferelden - it was all he needed to feel his life was worth it. In the end, letting him sacrifice himself for Ferelden seemed to do alot more good to him than letting him live while having lost perhaps the only opportunity he would have of doing something for Ferelden that'd be in the same level or even beyond the mistakes he made. And it didn't seem like something that just my character seemed to think was best for him: it seemed to be what Loghain himself thought was best. It didn't feel to him so much as if he was deciding what was best for Loghain, as it felt to him that he was acknowledging what Loghain considered best for himself. There are fates worse than death - and death at such circumstances seemed to be precisely what Loghain needed to get exactly the closure to his life that he wanted. And, beyond what was good to Loghain, it was also a way to redeem one of Ferelden's heroes - a way to make Ferelden not lose one of it's rolemodels of inspiration and belief in their nation, one which wouldn't be achieved through illusion, but rather through an actual redemption of said hero. So, finally, my Warden decided to allow him to take the final blow.
Were these the best choices I could've taken with my character? As I said, there's plenty I wonder about when I think about it - specially because, as it happens the most, the first playthrough is the one in which you make your character choices based on the choices you would make. Sadly, a lot of game restrictions and mechanisms make it hard to do everything the way one would've wanted to, with just as much attention to the details or with as much exploration of the possibilites as one would've desired. Nevertheless, those are the choices I deemed best in my first playthrough, and some of the main reasons why I took them.
P.S.: Sorry for the massive post.