I'm a devout Andrastian mage, and Solas is a pro-free-mages. If I consistently tell him that I want all the mages back in the circles, he will disapprove strongly and eventually leave my party (which is a story outcome I don't want). I can lie to him about my plans for the circles and avoid him leaving the party, but it will contradict my RP goals, as a devout Andrastian is disgusted with lying. While being a devout Andrastian non-mage, Solas would still disapprove, but not so strongly and won't leave my party (as he knows that you can't expect from a non-mage person to fully understand a mage, so he will tolerate my views). That kind of mechanism would surely leave me regretting choosing a mage class :-P
FWIW, the way I dealt with this issue is to simply never talk to Solas.

He still disapproves of some decisions, even when he's left behind, but if you never talk to him, the disapproval check that causes him to leave can never happen (I think).
Eh, I think that for the first PT I will stick to a warrior and leave mage for a second PT.
Let me bother you guys with some more qestions, as your advices are priceless: does reaver specialization stick with devout human Andrastian? I mean, are there serious and numerous NPCs reactions to specializations? Should I expect someone to tell me "OMFG bro, you are herald of Andraste and seemed so faithful, yet you became a dragon-blood-drinking-crazy-close-to-a-blood-mage-killing-machine-monster??? WTF is wrong with you???!!!"
My opinion is, no, devotion to Andraste is antithetical to Reaver specialization. I mean, consider DAO canon. You have to defile the Sacred Urn of (Andraste's) Ashes to get Reaver skills! I think that's pretty clear cut.
But, as noted already, there is very little reaction to your specialization choices, whatever you choose. You'll get more comments on who you romance than your dragon-blood-drinking-life-force-sucking rampages.
Champion seems too boring for me and I prefer DPSing over tanking. Templar seems like an ideal choice - interesting gameplay (that eldritch combo seems fun) and correct with story and set RP, however, I fancy the "high risk - high reward with high DPS" playstyle, and additionaly those animations of dragon attacks look really nice. What do you guys think?
It's hard to say. I thought 2H warrior would be boring, but I'm doing a 2H Champion Qunari playthrough now and it's really fun. I hate to agree with the sarcastic post above, but it's true, you won't know until you try it.
Champion is the safest choice RP/story wise. If you go Templar, you put yourself in the middle of the mage/templar conflict and have to navigate your way through that mess, though I can't say for sure since I haven't played Templar as IQ.
The good thing is you don't have to worry too much about missing out on something, whatever you decide. You get all the classes and specializations in your party, so you can try them all out if you want. I played as Solas for most of one playthrough because I just really liked Rift Mage. My IQ (DW Tempest rogue) was relegated to sneak attacking on automatic, until he leveled up enough to make Tempest playable.