I'm big on the free travel, so the rate at which that can be earned (with bonus miles due to status being a big part of that) is probably #1. OTOH, an LCC with generous in-network awards still would be highly unlikely to steal me away from a global alliance because I want the destination selection. Upgrades are also good and will break any tie, though I never spend miles on them.

All in all, I think people will fall into either the "upgrader" or "free-travel" camp, and I'm in the latter.