I generally go to two, rarely three a year. Guaranteed I always make it to Otakon, and often enough I go to Zenkaikon since (until recently) literally just a 20 minute drive from my house. Shame the VFCC had to be renovated and turned into a casino... Now the convention is way out in Bumblefuck, PA. Last year I ended up going to Katsucon. It was fun so I might go again sometime.
I'd really like to visit more conventions, because they are great ways for me to actually see my friends, but sadly they are kind of expensive.
Katsucon ~ Zenkaikon ~ Otakon