Wheel size opinions?

[speednr1]

I am sure its been beat to death, but I searched and didnt get the answer I wanted.
with that said, What size wheels would you choose and why?
My delimma is to keep the nice kmc 17" wheels that are on the truck now, or have the dealer put the stock ones back on before delivery, then get different ones?
so should I stay with 17" or go up to 20" thanks. pleae tell me why if you will