I'd run the 18. The 20x12 will be out past the ADV fenders even with stock suspension.
The 18x10 comes out 4" from stock.
The 20x12 comes out 5 " from stock
It's your truck and you get to pick the look but adding two inches of width via fenders just to have the new wheel stick 2-3" past them doesn't seem ideal.
yea i still havent fully pulled the trigger thats the one issue im worried about is the wheels sticking out way too far past the new fenders