If you don't want to do any clutching you will need to go with 26inch. As far as the which tire, I will let the other guys help you decide.
I just realized I typed Mudzillas in my original post, I meant Zillas. I had 28" Mudzillas on my previous Grizzly, they were complete OVERKILL for what I do (although they looked cool) I appreciate all the feedback, I think i'm leaning towards the ZillasThe Maxxis Mudzilla's are full dedicated mud tires, and one of the heaviest per size on the market. You do not want a set of these for your uses.
The Maxxis Zilla on the other hand is a completely different story. This tire will be excellent for you. Very light. Good tread design. Overall a great performer.