wow has a story, but its insanely long and you get that ****** off, i haven't finished it, feeling however you play and it gets soooo boring. 2142 is for me better than most people seem to think. but its so random, good games compared to bad. so many servers can be good but if you get 31 crap opponents, or 31 people with a crap ping, or a team that won't work together against a team that will. cs is less team dependant, you can go on a good run and win a map on your own, because its shorter than 2142 really and the opposition won't all play as a team either.
get all three, play all three in rotation so you don't get too bored of one or the other. theres a couple of fps based mmorpg's coming out in the next year i think. one of the things about grinding in WOW is that its a click action game, you can't aim your bow or your special shots. so an fps based version where aiming is down to your skill and you can have a much more hands on active hand in battle sounds like a good combination added to in depth story and longetivity.