I will analyse the main characters from each. That is what should sway me into preferring one or the other.
KOTOR 2 - The main character is very weak. Considering he fought on the frontlines alongside Revan, he should be a very powerful person. However, I do understand that he lost the Force, don't misinterpret me on that. It is once he regains it that he is a weak character.
My characters' discussion choices are very limited to that of a very naive Jedi or an extreme darksider. I have high Wisdom and Awareness, so that isn't the problem. I find irritation in the fact that my character shows so much naivety. It could be said that forgetting the Force is very difficult, but my "Exile" pulled it off superbly. He always has choices that either kowtow to another party member, which certainly lowers the characters' influence over others, or ones that I morally wouldn't choose in his position. I began to get frustrated that my character is captured so many times; something that is natural considering the bounty on his head, but surely not considering the guys' power. I mean, come on! Isn't he supposed to be saving the pretty women, rather than the other way around all the time?
The character in KOTOR was much more alpha-male, powerful and protective of his party and disciples. The range of decisions available were (unfortunately) not down mainly to skill at certain attributes, but they were still better than in the sequel. The revelation was masterful; certainly a little predictable with hindsight, but absolutely excellent. I saw my character in a new light after that, shifting to power battles with my lightsaber from the more Sentinel-like stance.
The main character shapes the game. The idea of a RPG is that you control someone else with the credibility to ensure that you can actually *be* the character. All other characters, environments etc are irrelevant. For that one reason alone, KOTOR 1 was a better game. I am still proud of Obsidian for releasing such a brilliant game, though.