Our local tire dealer who moves a ton of tires runs them on both of his service trucks and says from what he's seen on customers trucks the MTs will outlast other mud tires.  They are expensive but he said for guys who overload their trucks, run on alot of gravel roads and don't take time to rotate their tires they last enough longer than other mud tires that their cost per mile is cheaper than cheaper tires. 

I have Hankook RTO3 tires on my truck and my Tracker, they aren't as aggressive as the Firestone MT but I think they are a nice middle ground between an AT and a MT tire.  From what I've seen so far with 30,000 miles between the vehicles I will probably go with the RT03 again since I don't need a full blown mud tire but need something more aggressive than an AT tire.