I guess I do prefer KOTOR for the replayability it had, and I know I would have enjoyed it more if the surprise had not been revealed to me early (the Databank talks about you being Revan undirectly). I think it was a great game, an excellent storyline done with much imagination, and very enjoyable.
KOTOR 2 disappointed me at the end, as it did us all I think. But the second time I played it, I kinda understood more the storyline, I went deeper with each character, and explored every world with more enthusiasm. I like the "dark" tone the game had, with all the "hidden" Sith and the betrayer. I guess I'm a fan of plot twists like in K1 and the Traya thing in K2, and I still like a lot that part when you are talking to the Jedi Council, and the dialogue alternates between them and Kreia...
Well I guess it depends on each person's own opinion and likes. I did enjoy K2, and still enjoy it a lot, as I did K1. Of course K2 could have been A LOT better... but those hopes remain in the hands of TSL Restoration Project (thx 4 that).