1. Predator 2 Elder
2. Predator 2 Battle damaged Sideshow exclusive
3. Predator 2 Pred
4. Ani-Com Scar.
5. Wolfie
6. AvP Scar (reg)
That'd be my take on popularity. Even though I don't have a Pred 2 Pred, I am going on how good the Pred 2 Elder is. So I can see the appeal, particularly of the Sideshow exclusive. I'll have to see the Wolfie first hand, so I'm judging that on how Hot Toys seems to be doing these better with each issue.
Demand, not sure what you mean entirely. You can only get what's available and only if you're willing to pay, virtually the pre-order cost, or are prepared to pay more later. I haven't investigated their rising value, to any extent, but the AvP Scar (reg) really seems to have shot up enormously.