Search and you'll find tons of stuff on different tires here.
In short, true Mud tires like BFG, Maxxis Buckshots, and such are going to be quite loud on the road. I ran mud tires for years on my old Tacoma. Even rotating them every 5-6k miles, they will still cup and become loud. I would guess the most miles you'll get out of a set up mud tires would be 30-40k, I averaged 30.
A/T tires on the other hand are just a touch louder than stock/street tires. There are some out there with a 50k mile warranty. BFG A/T's are known for long tread life at 50k + and they look cool, however they have there drawbacks. Not good in mud, tend to hydroplane, and very expensive.
After running mud tires for so long, I can say I do miss them, but only on a couple occasions per year when I'm in some sticky muddy duck hunting situations.
Bottom line, unless you spend ALOT of time off road I would stick with A/T. Some guys will tell you different, but your 4runner will be rougher and louder w/ the M/T's. Hope that helps!