Boxing, kickboxing, or other?

I want to learn how to fight overall (mostly for defense since I am extremely friendly and avoid fights at all costs), want to get a great exercise, want to get tougher, vent, and want to have fun. So what is the best way to have fun and get a good workout but learn to fight at the same time? A challenge would be good too. I like boxing most but I would do whatever teaches you best.