Well there are basically two scenarios in Urban Warfare (sure there are more, but this is a simple breakdown).
1. Everyone you run into as enemy. That is, all the civilians are gone/dead. Everyone left is a hostile with intent to kill you.
2. You have to figure out who is good/bad before you kill them or they kill you. Killing good people is extremely bad. You getting killed is extremely bad.
In the first, I think we would do extremely well. Against a clear and obvious foe I think our military can excel.
In the second, you would have things like Vietnam and Somalia all over again. Casualties would be high, because the US is not allowed to kill civilians otherwise all hell breaks loose in the public and international relations. Here I think the regular military would have problems, but the special forces groups would be more likely to succeed, mostly due to their small unit sizes.
But this is completely my opinion and based on little fact. So take it as you will.