depends what you like really...not gonna talk about f2p mmos, coz they generally suck and for most, if u wanna be competitive, you'll end up paying more than the subscription per month.
if it's the classic fantasy rpg with trolls, gnomes, dwarfs and tree loving elf hippies, wow's honestly the best.
aion is a grindfest (srsly, didn't play but heard it's grind paradise...like hardcore legend of mir or other korean mmo grind), age of conan is shit (still, which is kinda amazing), haven't played champions online but i hear it's meh, LotRO seems to be heading in the right direction after a somewhat disappointing start, so you're left with warhammer, which i keep hearing from friends that it's quite a good wow copy.
if orcs and gnomes are not a requirement and you are above 18 years old, play eve. best game out there imo, from a design and gameplay perspective. most would agree it's right there after wow, on #2. free expansions coming out twice a year, new gameplay mechanics out regularly (not the same arena, bg, instance, raid gameplay with a new layer of paint). if you are capable or making friends, just do the tutorials and in two-three months you'll basically be doing end game shit. or in about the same time as your average MMO.
and if nothing pleases you, wait for APB, which should hopefully be just awesome. it's seen a lot of praise, but probably worth it...tho i'm a bit concerned by the fact that the release date has been pushed back a couple of times already.
TL;DR: wow's the best, then eve, then warhammer and lotro...f2p are shit
PS scratch lotro, they're making it f2p witch means you'll have to buy shit to enjoy the complete playing experience.
so TL;DR2: wow...if not, eve...if not, warhammer...if not, wait for apb...if not, don't bother really
