1) Strength in numbers. There are way more MUSCLE/Kinnikuman sculpts than there are BBs.
2) Variety. MUSCLEs not only have anthropomorphic animals like BBs, but also plenty of other themes... aliens, buildings, rocks, household objects, etc.
3) Cost. MUSCLEs are much less expensive to collect than BBs (not including Super-Rares, of course).
4) Durability. I'll disagree with Philly here. I've often seen BBs with their arms broken off. You never see MUSCLEs in that condition unless someone took it upon themselves to do the poor MUSCLE in.
5) Extensive merchandising. MUSCLE/Kinnikuman is a separate entity, so there's a lot of cool merchandise to collect. BBs are a subset of the TF line, and there's much less in terms of merchandising.
6) Video games. Sure, the first MUSCLE NES game sucked, but the Ultimate Muscle game for PS3 was pretty sweet. I've never even heard of a BB video game.
Hm. That's all I can think of for now. Make mine MUSCLE!
