Compatibility
I think Budokan is right on target with his advice. I would just stress that the style of the school needs to be compatible with your interests. I do not mean martial style.
After viewing the class ask yourself if the structure is too strict or too lax. Is the instructor engaging, i.e. are the students paying attention to them? And lastly due the other students seem like people you want to hang out with? You are going to be spending a fair amount of time with them.
Good luck in your search and remember that it doesn't matter how good the lineage of a school is or how effective the Art is if you don't like the instructors, class format, or fellow students and drop out.
"I believe that, in a stupid society, intelligence is useless." - Shen Congwen (My Education)