For 33x12.50 and 35x12.50 tires, you're much better going with a 15x8 wheel if you offroad and air your tires down. A 15x10 wheel is ok for strictly street use but if it's for both street and offroad, go with a 15x8. Backspacing can be anywhere from 3.75" to 4.5" though you'll probably need a washer or two under each of the two steering stop bolts if you have 4.5" of backspacing to prevent minor tire rub.
Why 15x8 for 12.5" tires that are used for offroading? Because we air our tires down for better traction and to help protect the tires from damage, you'll quickly learn you can safely air down to a lower air pressure without the tire losing its bead (unseating) with a 15x8 wheel than you can with a 15x10 wheel. Why? Because it takes less air pressure to hold a tire safely and securely seated against a wheel whose edges are only 8" apart than if they are 10" apart.
The vast majority of knowledgeable offroaders running 33x12.50 or 35x12.50 (as I run) do so on 15x8 wheels.