v8. You will only get 17mpg w/o AC, but the extra power you get is awesome. The v6 will work fine, but my v8 has better power up hills, in 4x4 and on the highway.
Thinking about getting the Toyo OC AT II very soon. Although, I have read many reviews of them being loose in the snow and prone to hydroplaning. Seems crazy, but worth asking. How have they been for you?