Rarest figures: well that depends on your point of view . . . . .
I have a couple vintage Boba Fetts that have variations of the original colors on the body. Some say this happened over time, call it fading; but if I show you pics you would see the colors may be different only at the torso or the arms, etc. It isn't an overall color change, there are distinct colors as though the plastic had some color go thru that wasn't supposed to. I am told if it were the degradation of the plastic, and it was fading, that it would also have a sticky feel to it. These do not.
As for the more recent items, I have a Commander Fox in a starcase, and the latest hoth pilot Luke, which is appears to be rare at this time.
and then of course there is my rebel pilot collection and astromech droid collection . . . . ok well so much for naming one!!