I already own a 360 and a wii a couple of my freinds own ps3.
doa4 online for xbox
virtua fighter 5 online xbox
virtua fighter 5 not online ps3 (feels like playing DOA1 to me but some may like it better than doa4)
both have emulation for some good fighting games dont know off hand which has better.
soul calibur is duel system confirmed
king of fighters xii is confirmed duel system
doa5 could go either or duel system (ninja gaiden 2 xbox exclusive, but im betting duel)
tekken 6 ps3 exclusive
guility gear 3d game confirmed xbox exclusive.
ps3 has backwords compatalitity to all ps2 fighting games (basically every good fighting game -doa3 to come out in the past 10 years)
xbox 360 has backwords compatabiltiy to only some xbox fighting games (no capcom vs snk 2 grr) some are online(few have anyone playing maybe guility gear and and street fighter anniversary) practically no ps2 are
Ps3 has bluray which doesnt make a large diffence to a fighting games. but if your getting an hdtv and a sound system ps3 is a dirt cheap blueray player and that is huge incentive.
xbox you have to pay for online service
some kick ass games are coming out for ps3 including mgs4 and final fantasy xii exclusive (im sure microsoft is trying to get them duel system and could potentially suceed like with others)
xbox has some awesome shooters
the creator of final fantasy now works for microsoft.
xbox is a joke in japan could definatly could harm the console in the future( i think things could change (and have been) but if they dont ill have to buy a ps3 before ps4 with backwords compatability comes out next generation.)
if you dont care playing fighting games online and dont like shooters than ps3 is probubly a little better
so basically for the near future xbox 360 is pretty superior but in the future the lack of a japanese market could hurt. final fantasy xiii and metal gear as exclusives is a huge deal to alot of people
in the long run it could go either way, xbox has the japan thing, and ps3 currently isnt doing so hot if it doesnt build a decent base it could keep losing exclusives and eventually not be developed for as much and be like xbox was last gen.
if you didnt own ps2 id say buy ps3 for sure cus there are so many good ps2 games that could keep you busy till ps3 picks up steam.