Fortunately, here in WY we don't have to worry about fender coverage. I have 3.5" back spacing on my 15" x 8" wheels & no suspension rubbing issues even at full stuff, etc. I did have to trim the stock fenders 1" for max articulation. The only downside is that my jeep gets filthy if I even think about driving through a puddle.
That said, I think the 3.75" back spacing is more common, but 3.5" works well too, especially if you want as much articulation as possible without rubbing.