Pretty much all of those games are empty wastelands on XBL...
They've ether had sequels that the only community moved to or they were never very popular and have been out so long that the few people they had got bored.
I can't really comment on TS2 or BF2 but I've played all of the racing games you listed
PGR 3 - a cross between a sim racer and an arcade racer, arcade fans will say it's too sim like, sim fans will say it's too arcady. I like it personally, it's an acquired taste. The game is quite challenging, and you'll need to play the same races over and over again to get the achievements. Online has some really neat features and fun modes... but don't expect to find anyone to play with...
NFS Most Wanted - the game is fun for a few hours then it gets repetive, you can beat the single player inside of 12 hours, and even when the game was new there was hardly anyone online... don't waste your money. this is a rental for a quick 1000 points, nothing more.
Ridge Racer 6 - very arcady, drift racing, all fake cars. You either like ridge racer or you hate it, there's no middle ground. Personally I like it. Single player campaign has close to 300 challenges and the game is HARD... like REALLY HARD. Online is probably more vibrant than any of the other games listed here... even recently I was able to find one or two rooms with a few people in them, but the people that play online are stupid good, and unless you've beat single player mode and unlocked all the good cars you'll get completely owned online.
I actually like RR6, I like PGR3 better but RR6 will last you longer, it's mostly a matter of tastes really. Don't expect to get the full 1000 in RR6 anytime soon either. I've had it pretty much since launch and I still don't have it, though I'm getting closer.
MyGamerCard.net has a neat feature call the "Live Tracker"
http://www.mygamercard.net/tracker.phpit tracks what people are playing online right now. It only tracks people that have signed up to be tracked (myself included) but it gives you a good idea of which games are popular and which games aren't.
Honestly if you want a quality online experience that will last you well over a year with lots of people to play with.
the best tennis game to get is Virtua Tennis 3
the best shooter to get is Halo 3 or Gears of War
the best racer to get is Forza 2
those games cost more than $25 but they'll get you your money's worth.
This post has been edited by twistedsymphony: Jan 23 2008, 03:47 PM