I'd say BG II is timeless, but personally I can't go back and replay it because of its graphics, lack of voiceover etc. That being said, I feel the game is a little overrated, it was very good, excellent, but if you read some comments around the 'net you'll think it's better than driving a Porsche, with Megan Fox on the seat next to you.
NWN2 OC is good, MotB is very good, SoZ & MoW I haven't played yet. NWN2 also has a plethora of mods, some of which are pretty good, one I'll be playing soonish is Pools of Radiance's remake. You may also want to keep an eye on BG I remake project - their screenshots were good enough to make me buy SoZ while waiting for release. I'd say mods are like having a huge breadth of DLC at your disposal. Also, imho, if NWN2 didn't have so many bugs on release, I think it would have a reputation as good as DAO, and it's a shame because the game is pretty stable nowadays.
Comparing BG II to NWN2 is tough, they're similar games but with almost a decade separating them, overall as a game, I'll have to go with NWN2. However, if the question was, which game was best *for its time*, I'd go with BG II.
If I had money for just one game now, I'd pick NWN2+expansions, I find it hard to believe that someone can get into BGII especially if (s)he hadn't played it back then, great game but gaming is at a different level these days.