I'm actually going to follow the crowd here - FF would win.
Mr. Fantastic could run Batman through hoops trying to figure out how to counter the him while still building a device that would nulify Supes powers (if it's the JL:TAS version - a fly swatter might work). Invisible Woman would truly hold the edge over WW and Hawkgirl. Human Torch - Martain Manhunter would run away crying for his mommy, nuff said! Thing could take on any power they have and one hit from him would take out the Flash (who would probably hurt his hand at the same time from trying to beat up ol Grimm). The only one that could pose a problem would be GL but since his power relies on concentration it would be easy enough for Reed to rig something up that would effectively cancel GL from even being a factor.
"Never give in--never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honour and good sense. Never yield to force; never yield to the apparently overwhelming might of the enemy."
- Prime Minister Winston Churchill
"Si vis pacem, para bellum."