Yeah, I'd more say Alistair was more Loghain's direct enemy then yours (save for the City Elf and perhaps the Human Noble). For the human noble, Howe is more of their 'enemy', while the Archdemon was the final act. I find Loghain quite an interesting character, but unless I was playing a gung-ho Grey Warden, he really wasn't my 'personal' enemy so much as yet another jerk getting in the way of ending the blight so my character could move on with their life.
(To be honest, I found for Origins, Dwarf Noble versus Bhelen had the greatest amount of tension: he screwed you over completely, had your other brother killed and framed you, your dad seems to have died of heartbreak (if not poison) due to it all, and yet... he's managed to completely outplay you, and will probably do damn well ruling the dwarves.)
(And then, you know, he does. And unlike Harrowmont, who purposely makes your statue smaller then the other paragons (jerk!) and declares you dead, your bro (or even brother-in-law!) is still firm in the belief that you're still out there and is apparently still holds some fondness for you.)
Anders and Hawke is probably also an owch, because if you're unspoiled, it's pretty much unexpected- and if you were romancing him, well, owch. That I would say is possibly the most interesting, as it's pretty hard to play through the game without getting Anders mostly to either rivalry or friendship unless you're trying to keep him neutral and ignoring him... so he was something to Hawke, be it friend or rival. That's personal.
Other then that, yeah, I'd go for the Architect. Not only is he interesting (like Loghain), but unlike Loghain, I felt like he was more distinct in giving me a way to be interested (Loghain only offers me 'another warden to throw at the archdemon'- which, I mean, I already have Alistair if I need that- and only builds up my hate if he's trying to enslave my characters family and friends). The Architect could be the key to stopping blights... yet he also kidnapped my character, stripped her, and stole her blood for nefarious purposes. The more we learn about him being one of the Magisters, the more interesting it gets.