It all depends on your goals.. Do you want to fight in the ring? Get in shape? or just be an all out bad ass. If getting back in shape, and losing some weight is your goal then any martial art system will work along with a decent diet. Want to cage fight? Then learn BJJ, Muay Thai and wrestling..
Like Rick said, Krav Maga is a great system for self defense. It's a proven and battle tested. All of the other disciplines are "support" systems for KM.. Krav Maga is about doing anything you can in a fight to survive.. eye gouge, throat hits, strikes to knee, rip ears off, bite, grab balls and pull, use things around you, etc.