Go 18s, and get Nitto Terra Grapplers. I run them (on my Jeep and the LR) and they do great for an all terrain. I've used them in the Rockies, Applachians and down in swamps in FL and they do great for an all terrain. Mud, like any AT, they can get a bit clogged. Just my opinion...Duratracs are a soild bet too.
recently put the TerraGrappler G2s on, and with 6k miles and some off road time, I gotta say they're pretty good.