BF2 = best multiplayer game ever. Don't bother with 2142.
If you buy BF2, you definitely will still find a lot of people playing.
But trying to get into it now will be quite the challenge because the people who are playing now have been playing for a loooooong time. They probably have really high ranks and all the unlocks, and they know the game like the back of their hand.
I used to be one of those people until I stopped playing. I tried going back recently and failed terribly.
That's the biggest draw back to getting it now. It's like someone who never played Halo online... or someone who's never played Starcraft jumping on to battle.net looking for a game. You're gonna get rocked.
If you do manage through it though, you'll find yourself playing one amazing multiplayer game.
Oh yeah, also the game doesn't have true widescreen support and never will. It can run at 1600x1200, but it's literally just stretched to fit. That was really annoying for me.