Martial arts are fun if you have a friend who's passionate about it, and is willing to walk with you through it. I had significantly more fun learning karate than capoeira, despite more interest in capoeria, because I could practice and have fun with my friends while doing karate.
I took gymnastics for a little while when I was younger, but my body wasn't too suited for it, so I can't give an accurate description for how it's like. It looks like it'd be fun though, but I'm not sure how it compares.
Breakdancing is shit-tier. Don't do it. All the d-bags I know try to show off with it. Quite honestly, it looks stupid more often than not.