This is a difficult question for me. Ultimately I decided on
SoA, but
BG nearly beat it out. It really came down to characters vs game design. The biggest mistake, IMO, that was made with
SoA was taking the game all the way to level 20(ish). The original showed admirable restraint in sticking to low level play, and that is a feat that Bioware never duplicated afterward in any of its franchises(lol at Shepard being level 1-5 at the beginning of ME2). I think that
ToB would be a far more enjoyable experience for me(not that it's bad as it is) had
SoA ended at around level 15-16 and let
ToB take things from there. Additionally, I think that I prefer
BG's exploratory travel style, and I remember the twinge of disappointment I felt when I realized I could only go to specific locations in
SoA. They both may have been fairly linear games, but I feel that
BG did a good job of hiding that fact.
But then there are the characters. Between the romances, the banter, the personal quests, and just the personality that some of these characters had, there really is no comparison between the two games. And in the end, that's what keeps me coming back to play the games year after year. Minsc, Haer'Dalis, Viconia... even Edwin... They're like old friends that may not be part of your life anymore, but always make you smile when you have a chance to visit. And that's why I pick
SoA as my favorite part of the saga.