anybody have an opinion? 18" wheels vs. 20"

I prefer 18 wheels on my F-150. Greater tire selection, a little lower in price, more air cushion/less bent rims from hitting pot holes and better for off-road travel. My selection is based on use, not looks, although I don't think the 18" look bad at all. I consider 20" wheels to be for show and street use. The heavy duty F-150 comes standard with 17" wheels. That should tell you something about wheel/tire size based on use. To each, their own.