Ya know this is a lot harder than I thought it would be. So many great fighters on that system. I'd say out of ones I own I'd have to go with:
Galactic Wrestling Featuring Ultimate Muscle (too bad my ps2 has trouble reading this disc now
)
PS: This is what I own:
Art of Fighting Anthology
Capcom Fighting Evolution
Capcom vs SNK 2: Mark of the Millennium 2001
Dragon Ball Z: Budokai Tenkaichi 2
Fatal Fury: Battle Archives Volume 1
Fatal Fury: Battle Archives Volume 2
Galactic Wrestling Featuring Ultimate Muscle
King of Fighters 2006, The
Mortal Kombat: Deadly Alliance
Street Fighter Alpha Anthology