Personally...I would go with a 20" or 22" wheel. I can't stand the look of a 15" wheel surrounded by a huge tire like a 38". It reminds me of a setup that belongs on a mid-80s 4x4 Chevy or something. Not a good look (again...just my opinion) for a new F250 4x4.
I run 24" wheels with 35" street tires on my 2008 F250, and I think it looks awesome. I will probably add another inch or 2 in lift and go with 37s next year. But for now...I like this look:
