Top tier boxer against top tier MMA, the only situation a boxer would win in, would be a boxing match. MMA style, street fight, wrestling, any other sort of fight, the MMA fighter would absolutely dominate.
I enjoy mma, and was doing "mma" before it was called "mma", as I have been involved in martial arts for about 20 years. I trained mostly in "non-traditional" arts. All I can say is, it is silly to make such blanket statements as the above post. You have to look at the ATTRIBUTES of the fighters you are dealing with, not just their so-called skill set. Are these mma fighters you speak of in great condition (because they aren't always)? Is the boxer a naturally gifted athlete, or just someone with "heavy hands"?
You are going to tell me any mma fighter would "absolutely dominate" an in-his-prime Tyson, Benard Hopkins, Shane Mosely, or any number of other boxers in a street fight? Seriously, you don't know what the fuck you're talking about. Boxing is a HIGHLY effective form of self-defense for the streets. It may be limited in its arsenal, but on a concrete sidewalk or alleyway it isn't exactly the best idea to be fighting on the ground. Standing toe-to-toe with a professional boxer could cause you to get knocked out without you even seeing the punch coming. And having sparred with a couple of professional boxers, I know how hard they can be to even hit once, given their hand and head movement.
In an mma fight, the mma fighter clearly has the advantage. Logic should tell you that. In boxing, the boxer would have the advantage. Again, that is simple logic. But on the street where ANYTHING goes? It's the attributes of the fighters that will be a huge factor. A young Tyson in a street fight would bite CroCop's nuts off if he had to before punching Mirko harder than he has ever been hit in his life. I am not saying Fedor or CroCop wouldn't stand a chance...of course they would. They are tough guys with a lot of ring and cage experience. But never forget, UFC...PRIDE...BoreDog...
IFL...these are all sporting organizations with rules and regulations. A streetfight IS NOT A SPORT AND THERE AREN'T ANY RULES.
That said, I'm done with this thread. These kinds of debates go in circles and most don't listen to those who know.