hehe.....I have extensive experience
For open field mud running, as much as it pains me to say, you can't touch a big beefy long wheel based truck with 38inch or better tires.
For super tight wooded trails, you can beat a little 4 banger jeep with 31-33 inch tires. Its light, leaves little foot prints and is highly manuverable around the trees and stumps.
For more used trails, rocks, stream beds, etc...a nicely setup jeep with a 6 (or 8 conversion) and 35 inch tires is hard to top. Not too much lift to make it overly top heavy, plenty of grip, lotsa torque, and the short wheel base makes steep embankments dissappear. I ran my truck up a steep embankment from an old crick once and literally put the rear bumper on the ground (dragged it for a good 12-16 inches before the whole truck was on the hill and scooped up about 50 pounds worth of sand/pebbles/dirt), put an air bubble in my fuel lines, and bent an exhaust pipe, the same slope was nothing to the jeep.