Definitely consider all aspects, like skill level, people, location, atmosphere, etc., etc.
Here's what I did. I checked out five and tried three before I decided. Don't feel you need to rush and decide after one or two classes (but don't wear out your welcome either) - if you're pressured to join any one class, don't. And don't make any long-term commitments to begin with, like paying for six months or a year in advance - many people drop out after a month or so.
One benefit I found with trying a few different dojo, is that I can drop in to visit/train with them all (probably could anyway).