PS3 provides more Diversity than any other system available.

[NSS7]

Tie = 0.5
Win = 1.0

Released games


JRPG = X360 win (SOIV, TOV, IU, TLR)
SRPG/ARPG = PS3 win (Valkyria Chronicle)
WRPG = X360 win (Mass Effect, Fallout DLC, Fable 2)
FPS = Tie (Killzone 2, Resistrance 1 and 2 vs Halo 3/ODST, L4D)
TPS = X360 win (Gears 1,2)
Racing = Tie (GT5P vs Forza 2)
Beat-'Em-Up = Tie
Fighting = X360 win (DOA4, 2 Naruto games)
Platformer = PS3 win (R & C: TOD, LBP)
Action Adventure = PS3 win (MGS4, Uncharted, Infamous, Yakuza 3)
Simulation = Tie
Sport = Tie

PS3 = 5.5
X360 = 6.5

Future games (announced games only)

JRPG = PS3 win (WKC 1 & 2, Aterlier, TOV and SOIV + new content)
SRPG/ARPG = PS3 win (FF Versus XIII, Demons Soul)
WRPG = X360 win (Mass Effect 2, Fable 3)
FPS = X360 win (Halo Reach, L4D2)
TPS = x360 win (Crackdown 2, Splinter Cell)
Racing = PS3 win (GT5, Mod Nation)
Beat-'Em-Up = PS3 win (Basara 3)
Fighting = Tie
Platformer = PS3 win (R & C: ACIT)
Action Adventure = PS3 win by longshot (Uncharted 2, Yakuza 4, Agent, GOW 1/2/3, L.A Noire, Heavy Rain)
Simulation = Tie
Sport = Tie

PS3= 7.5
X360 = 4.5

Conclusion
Right now X360 has more diversity than X360 but if you looks at future games PS3 definately triumph X360. Well MGS might announce more games for games in future. But right now PS3 has better lineup overall.