Put the lift on and get a quality drop hitch. The lift will make your truck handle differently, but you'll get used to it. I've towed with a 8" lift and 37's on a Tundra. Every vehicle I have owned so far has been lifted and I've towed thousands of miles without an issue. Sway bar will be mandatory and using common sense. One major downfall, the fuel mileage will suck! As to your original question, I like the looks of the 20's, but the 18's will probably give you a better ride. Also look at a Rough Country lift, I love their lifts.