I also agree on oberserving the instructors, in most cases you get a trial class and with this you can see the dynamic of the class and the dynamic of the instructor. Martial arts are great, but without the right instructor can be somewhat repetitive and boring. One thing I forgot to mention in regards to aikido is there's a focus on rolling and learning how to fall safely, something a lot of kids do not know how to do. I can recall a few times when I was a child and the rolling skills I learned from aikido came in handy, also one time probably saved my life.