Depending on how my right foot feels I can get 18 to 19 out of my 7.3l.
Not all 6.0s are bad. They had their problems but that is mostly from the headbolt isssues and egr issues. Yes a diesel may cost a lot more on parts but they are built to handle more abuse. Plus the big thing of a diesel over gas is the longevity of the engine.
I personally like driving my ranger and 250 just the same. But I really like me diesel more. I have used and abused the truck with working and engine mods. Its all in what you need the truck for. Just a daily driver with the occasional trailer tow you can get by with a gasser. If you must have a diesel and want mpg a cummins or duramax get better mpg honestly. I just love my Superduty more.
'04 F-250 King Ranch FX4
Tuned by Eric@ Innovative: tow, xstreet, xrace
Diesel Site Coolant Filter