TL;DW: Some microwaves have a popcorn button that just runs a timed cycle. Some better microwaves have steam sensors that attempt to divine when your popcorn is done, and a select few Whirlpool/KitchenAid models actually have acoustic sensors (microphones) that listen for the pops and stop the cycle when the popping slows down. Makers of microwavable popcorn don't know what kind of microwave you have, though, so they all warn you not to use the popcorn button.
I had a hot air popcorn popper as a kid and the popcorn was always way worse than the stuff from the cinema. Instead, get a big metal bowl and use the Alton Brown methode
I got the Presto Poplite and I've been very happy with it. Pretty straightforward. I don't exactly have a good butter distribution set up.. but otherwise I'd recommend it.
Altons method is very similar to the whirly pop, which was the other option I read about. For pretty much the same reasons Alton puts out: Thin metal, move popcorn, even heat distribution.
My old microwave made perfect popcorn in 2 minutes. The new one burns a bunch of kernels in 1m45s but leaves a shit ton unpopped. They're supposedly the same wattage.