Had to register to respond to this.
First of, from what I've seen, American Kenpo Karate seems like complete crap. Sure, that may vary a great deal but beware the Mc Dojos...
Then, there are very many different schools of Karate. I faced a similar decision like you and googled to find the strongest Karate. Internet told me that it was Kyokushin.
So I started doing Kyokushin Karate. My impressions are:
- Very good exercise for your body
- No clinching
- Little realistic practice of fighting with strikes to the head.
- Strong kicks, like in Muay Thai.
- Use of elbows and knees, like in Muay Thai.
- A lot of time is dedicated to learning techniques not for realistic use but for style and as part of learning the martial art.
- So far, being a beginner, not that much actual sparring.
I'm happy with it and will continue (been 6 months now). But if you want to get down and dirty from the get go then I suggest you pick something else. Kyokushin produces great fighters (given the rule-set) but the sparring is pretty different than in actual MMA because since no strikes to the head is allowed you stand really close to your opponent. Going from that to MMA would certainly require adaption. Also, since there is no real clinching you will have to learn that somewhere else...
But like I said, Kyokushin is really good.