If I didn't plan on towing over 6000ish lbs I'd seriously consider the 2.7. I think it can be equipped to tow somewhere around 7500.
There isn't enough difference in fuel mileage between the 3.5 EB and 5.0 V8 to worry about. If anything the V8 does a little better, especially when towing. On paper the 3.5 will tow heavier loads, but most 1/2 ton trucks run out of usable payload at about the same trailer weight. Properly equipped the 3.5 can tow 12,000 lbs, but tongue weight starts to limit things to about 7000 regardless of the engine with 1/2 ton trucks. Ford does offer a heavy duty payload package that adds 800 lbs of payload, but those trucks are unicorns. If you can find one, or order one, there is some overlap with some 3/4 ton trucks.
With that in mind the 5.0 V8 made more sense for me (mine is a 2014). The 2.7 EB wasn't available at the time. But if buying a new one today I'd seriously consider it. It is the fastest of the 3 engines, gets at least 2-3 mpg better fuel mileage, costs less, and will still tow more than most people will pull with a 1/2 ton truck.
