Another vote for a $0.05 brown paper lunch bag.
I picked up an air popper last year hoping to avoid the microwave situation where if you try to do too much at once, early-popped kernels end up getting burnt. Did not like! The air popper had a nasty habit of kicking out unpopped kernels that would then pop in the bowl, exploding popcorn all over the place.
I've gone back to brown paper bag exclusively, and just do a little less at once.