Site to bet for mma preferably single fights I don't like the draft kings where u have to pick for the whole card 
- which country ? US has different laws or something, so more complicated.
www.bestfightodds.com shows you the odds with several different online betting sites.
I'm in Canada, and use Bodog.EU, which is the international version of Bovada.com, which I think is available in the US. I'm happy with them, and withdraw winnings with them regularly (although it takes about 7-10 days). I'd recommend them.
folks here often recommend 5dimes.
if you want an account at Bodog (or Bovada), please use my referral code, so that I get a bonus for referring you. I think most sportsbooks offer this kind of deal, on top of a 100% deposit bonus for the new member, so it's free (extra) money!
maybe some folks on here can tell you more about 5dimes or other sportsbooks. I used to also use Sportsinteraction.com, but their lines are not as good (more juice), and it was more complicated to withdraw money.
if you pick Bodog or Bovada, here's my referral link : https://www.bodog.eu/welcome/P1CC7BAA/join/?extcmpid=rafcopy
actually, RE: 5dimes, scratch that. I wouldn't do any business with them : http://sportsbettingsites.org/news/5dimes-confiscates-over-32k-balance-2500/