The only thing that is guaranteed in a street fight is that it will inevitably end in a wrestling match. :deal
mma is a combination of styles, and incorporates boxing, wrestling, judo, bjj, muay thai, karate and so on. It is far closer to reality because it gives you a bigger variety of choices, not just having to punch but also to kick/knee/elbow etc. But all in all, it's not what you know, it's how well you can apply it with proper timing.
I do a bit of both. My first fight was boxing and my next one will probly be MMA. Obviously MMA is a serious discipline. They don't just hand out black belts in bjj and I know that from training with some little guys who are monsters on the ground. I tried fighting a few guys by myself once and I KO'd the first one and then took the second one down, it was all down hill after that. Having said that, mma basically has less rules so maybe it is better in the majority of situations. The Usain Bolt stratergy is the best one if your by yourself against a group of hard cases though.
It depends on the situation. For example, ever try getting a girl to make out with you after a snuff movie? :deal
If you're in a street fight you want as many weapons as possible. Let's look at two legends in both sports pretty much the same weight and pretty much the greatest of all time at their weights, middleweight Anderson Silva and cruiserweight Holyfield. Now, which guy would you rather be? Pick Holyfield and your ****ing mad. :nut