15 x 8 with 3.75 is the best choice. The backspacing determines how much clearance there is between the tire and Jeep components - in other words how far the tire is moved out. This is quite important with bigger wider tires to deal with rubbing issues. Stock backspacing is 5-5.5" which has the tire in much closer to the spring perchs etc.
8" wide wheels will hold the bead better than 10" when you air down on trails.
08 Grand Cherokee Overland