Shipwreck v1
Crimson guard v1
Destro v1
cobra officer v1
range viper
bullhorn
footloose
Recoil
Viper
Snake eyes v3

TOP TEN O-RING FIGURES:
By member votes.

Flint (5)
Falcon (5)
Viper (5)
Outback (5)
Snake Eyes V2 (4)
Crimson Guard (4)
Firefly (4)
Beach Head (4)
Major Bludd (4)
Night-Viper (4)

I tallied up the votes out of curiosity. I think it's interesting that other than one Snake Eyes figure, the characters that have the most versions and are always pushed to the forefront never made it on top ten. No Duke, Cobra Commander, Storm Shadow or Destro.