On both Ford and Chevy if you have a street side slide your ability to slide back/recline the drivers seat is going to be compromised. I'm 5' 9" and have no issues with the leg room in my 2012 E-350.
Another consideration is the drivers seat itself. The Ford power drivers seat is almost infinitely adjustable. Don't know if Chevy has anything comparable but I have sat in a Chevy manual seat and it is not fun, I can only imagine how not fun it would be on a long drive. After 6+ years and 60k+ miles I still have yet to get excess heat from the dog house. As far as mileage {expect 9 - 10} they are far more alike than different, mostly it depends on how you drive.
If your Ford {350 or 450} is properly aligned and has the correct psi for the load you are hauling there are zero handling issues. I've seen lots of folks throw copious amount of cash at the so called handling problem but mostly they are searching for a solution for which there is no known problem {the government does this a lot}.
As always... Opinions and YMMV