I use one class, and it nets me oodles and oodles of kills
Um....Primary doesn't matter, typically an assault rifle solely for the occasional long kill
USP .45 w/ Tactical Knife
Throwing Knife
Flash Grenades
Marathon Pro
Lightweight Pro
Commando Pro
Typically I'll get to 29 kills in FFA about 10 kills ahead of the next closest person, so I take my time and try to get a sweet throwing knife kill