I think Zedrush is probably one of the best guys to ask.
I've been doing Boxing since I was 17, I did do kick boxing for a little while and got to Orange belt, nothing special but if your dedicated you can fly up the belts, while I was at the club I also trained in Brazilian ju jitsu which is a very good form of self defence and fighting from the floor. It all depends what your after really, all martial arts are good for your fitness but it's really about finding the one that interests you most.
I've just got a punch bag in the garage at the moment, I try and train in there every other day but it's difficult with a new baby.
Hope you find something that suits you