For 31" tires I would definitely use a 15" wheel of your choice. 31s fit a stock Jeep with not rubbing. However many people do a. .75-2" budget boost which is spacers that sit on top of the coil and they also buy new longer shocks. IMO it looks pretty slick.
With 32" tire you're going to start to feel some power drain. Which engine, transmission, and axle gearing do you have?
Personally, I run 33x12.50x15 on a 15x8 tire with 3.74" backspacing, 3.75" of lift, and 4.56 gearing