Get the truck that tickles your fancy more than the other... :) The amount of 'towing miles' compared to 'not towing miles' is probably a lot, so your 'not towing miles' is going to be the more time you spend in the seat...
If mpg's is your concern and you need a truck, you can't dispute the Chevy's numbers... The Eco is right up there too, plus it's just plain fun to drive! :) Yes, I'm a bit biased on that statement, but it's true for me! :)
For me, my Eco is doing better on mpg's both towing and not towing compared to my 97 F150 and the 'fun factor' of the Eco is way beyond anything I've had before.... I had an 86 Mustang GT and that was fun, but this Eco would walk all over it!! :)
Good luck with the search and enjoy whatever you get! :)
Mitch