It depends what you consider to be "common", but according to YoJoe marketplace, the most wanted figs are:
- Cobra commander (common), position #3
- Viper pilot (rare), position #4
- Keel Haul (rare), position #6
- Grand slam (somehow common), position #8
- Shockwave - Night force (somehow common), position #10
- [...]
- Steeler (common), position #17
This gives us an idea...
That Cobra Commander is kinda surprising but I suppose I can understand since he was never released as a carded figure. I'd almost consider him a special case since he was a mail away or Sears exclusive.
Viper Pilot of course.
Keel Haul is unusual since I'm pretty sure he was available as a mail-away. He's certainly more common than the Defiant figures in my experience. (His gun on the other hand)
Grand Slam (Silver) was only available for one year I believe and people already had a JUMP so didn't buy another to get him.
Nightforce Shockwave goes for a lot for sure.
Steeler is a strange one. I'm pretty sure he's rather common BUT finding one with nice gold bars on the arms is pretty tough, and of course all of the straight arms were only available one year.