29" without modifications.., unless your coils, and leafs are lowering vehicle below oem stock, i.e., tired suspension.
AX-15 seems to be the replacement, albeit with some little complications that are little headaches, and time expenditures. Some say the BA-10/5 is junk, but mine has 200k and, knock on wood, still ok. Avoid speed shifting.
I've seen guys run 33s with no lift and tons of body modification...
I've seen enough rigs in person on 31s with little to no fender trimming. they rub like hell.
just think bump stops and lots of sheet metal cutting .