Typically, the better the tire is on the street, the worse it is on mud and vice versa. A good mud tire will (like Swampers, for example) is ussually louder than a WWII bomber, and a good street tire will ussually have no traction whatsoever in mud.
So the best compromise will depend on what you want to do, how often you expect to be on pavement and off it, what your noise tolerance is, and what you like as far as looks. This is a subject that has no correct answer, as people's uses and tastes are different...
Having said that, the best tire I have heard about for mixed use is the BFG MT, but again, that is subject to the tastes and preferences of the user. In my case, I am planning on putting a set of 33 BFG MT in my rig in about a year... Until then, I plan to keep on rolling on my 31s HT to wear them out a bit more.
Felipe