FFA would be best in teams of 4 or 5, one assault, one heavy, one med, one light, and maybe a nonmech asset.
That's just for no respawn game, because otherwise how would you not see all assaults in a dog pile of stupidity?
If you wanted a real ffa, have it like test of strength, limited C-bills but everyone against everyone with spaced but random spawn points.
Conversely you could have everyone start with enough for a medium mech, and thus lights, and most tanks. unlimited respawns but you only get the money you make off of damage along with shorter rounds; The scat spam I would imagine would be lame at the start though.
I wouldn't mind no respawn team matches, but no respawn ffa? Sounds kinda dumb.