Kinda off-topic, but it's not like we check any of the other parts of the forums. I've tried both, and it's hard to say.
I found Baldur's Gate II to have a steep difficulty and complexity curve, and usually I like that sort of game, but I lost track of the main story the moment I left the starter dungeon. Got killed by some vampires in the middle of the town (Is ANYWHERE safe?) and never played it again.
Flight Simulator X was great fun, but I couldn't find an affordable, compatible yoke at the time it was new. Also, the terrain was vague and the textures for the towns are a generic areal photographic tile repeated over and over. If they added a physics engine to Google Earth you'd get MUCH better results.
You'd probably get more enjoyment out of Baldur's gate. There is more variety in game play to be had, if you can tolerate the steep learning curve. Otherwise, go fly a kite.