While my rims are 11" and second set is 10", I also run a 15.5" wide tire. I personally don't like rims that are close to the width of the tire, looks funny to me. I like to see a fatter sidewall as this helps protect the rim while offroading, it also helps when you air down. More than that, I think it just looks better.
So I'd have to go with a 15x8 for the tire size you currently have. If you are towing more than anything, I think the wider 10" handles the weight better.
Here is my father truck with 35x12.5 on 10" rims. Next one is my truck with 38x15.5 on 11" rims.
