I have a good friend in IN who gets a genuine, documented 26 US mpg from his '00 F250 2WD PowerJoke, and I have the same engine/trans and can't beat 14 dead empty at the same 65 mph. I also have a small fleet of CTD3500s, and we get 17/18 US mpg beating the living crap out of them hauling junk through the mountains. Only a bit of D-Max experience, but from what I have seen, not quite as good as the Cummins.
So, for CURRENT US full-size: Ford could be very good, or it could be very bad...and the likelihood is that the 6.0 or 6.4 will blow up in your face many times. The Chevy engine is fine, the ride is incredible, but a manual gearbox ain't gonna happen. The Chrysler entry has the best power, best reliablity, best mileage, most available choices in cab/wheelbase/powertrain. Kind of a no-brainer.
What you REALLY want is no longer built: a 6.2 4x4, or maybe a 6.5 (better power, no better mileage). For light duty, these are great engines with low/mid 20 US mpg consistantly. Just try finding one.
The compromise would be a 12V with 5 speed 4x4 single cab. Lots of them around and dead cheap.