Play to your strengths, Grasshopper.
I'm not very flexible and when I was younger, had a very direct, straightforward approach to fights (i.e. "charge in with fists raised"), so Muay Thai really worked for me.
It's great for conditioning, there are no katas and with a relatively limited set of tools you really learn how to think on your feet.
But I've mellowed with age and am seriously considering Aikido. Love the concept of using the attacker's energy against him.
And lately, I've actually been training in parkour (the French art of "running away"). Yeah, it's not a combat art, but the approach and philosophy are reminiscent of martial arts, the community consists of a lot of martial artists and it will definitely get you in shape!
Point is, find something that works with your abilities and seems interesting and fun for you. Once you're narrowed it down, research some good places to train.