what two game fanbases would you say seem to hate eachother the most?

i might be fanning the flames here, but im in the process of writing a short film, and part of the plot is that there are two opposing factions of fans that are out for eachothers blood. now i was thinking halo vs killzone but if anyone else has any ideas send them my way.

Grand Theft Auto and Saints Row, Midnight Club and Need for Speed, Call of Duty and Halo, Forza and Gran Turismo, that's all I can think of for now.

virtua fighter vs. soul calibur?

Back in the day Mortal Kombat and Street Fighter.