Well 32's you are going to have to have some nature of lift or another way to deal with some rubbing if you don't have one already. In my experience, 32's are where you really start noticing the shorter gears becoming an issue as well. Basically less than 3.73's will start to feel slow. Advantages are a bit more underbody clearance, and depending on width comparisons, more contact patch.
i'm currently running 31x10.5 r15's on non stock rims (don't know dimentions of the rims) and don't have any rubbing.
any reason to upsize??
Some thoughts....Have you had any ground clearance issues with the 31"s (such as getting stuck)? If not, would it be for looks?
I had 32's years ago and was at point faced with an issue of needing 1 replacement and the only tire shop in town had to order it. (They had tons of 31's and 33's in stock). Just something to consider.
I had 30x9.50x15s BFG T/A KOs and I thought about going up to a 31x10.50x15, but I did side by side comparions at some local tire shops and there really wasn't much difference in size. So I looked at 32s and 33s. I think the 32s are about perfect (as long as you're not doing extreme offroading) I did alot of research on tires and their actual sizes (they're not always the same as they are advertised by the manufacturer). I found that the GoodYear Duratrac 33x12.50x15 is actually a 32x11.50x15 when it's mounted on a 15x8" rim and the psi is properly set. a 2" lift would be ideal if you just do mild offroading, if you think you'll get into more than the mild stuff, I'd say 3" would better suit you. here's mine with the Duratracs and one showing the new and old tires side by side just before I put them on.