Depends how heavy and often you haul... 155/30 is what most use that haul heavy and want that little extra. You can probably do 175's, just keep the nozzle size small. If you tow a lot and heavy, I'd just stick with stock honestly.
A good tow tune makes a HUGE difference in these. You can use the turbo as an exhaust brake (kind of), and the trans shifting is greatly improved. With my tow tune and tow/haul on, it's actually fun to yank stuff around.