Well for me best map for FFA is... Summit. Its beast. In FFA, all you gotta do is watch your back and memorize the spawns. Try going to combat training and play with bots in FFA. You would see where they're all coming from.
Suggested Class:
Primary: AK74u w/ Extended Mags (Who needs grip lol) or Famas w/ Red Dot
Secondary: Python w/ Acog sight (Its pretty good cause I dont like the iron sights for it).
Lethal: Frag or Semtex
Tactical: Concussion
Equipment: Claymore or C4.
Perk 1: Lightweight (Ghost is shit anyway. Get a blackbird and your solved)
Perk 2: Sleight of Hand
Perk 3: Marathon or Ninja (I use ninja cause I have a gaming headset. SOUNDWHORE <3)
Killstreaks?
Spy Plane or UAV
Attack Helicopter
Attack Dogs (Use Chopper gunner if its Nuketown FFA xD)