I think the 2.7 would be good if you towed shorter distances. I hear it’s comparable to a 5.0 or 5.3. But I think that engine would work harder.

3.5 is a power house.

I went with 3.0 1/2 diesel. I have been amazed at the towing performance. It does amazing in the hills.

I towed my fx20 from Abilene to fork for the Berkley and got 18 mpg. On the highway no trailer 25 mpg. Diesel is crazy expensive right now though.

I own 2 of the 2.7 Eco, in the FX4 version running 35's. . I love mine, I previously had a 5.0 which is great as well, but the ecoboost does all it is asked and more. I have owned a couple heavy rigs as well as a 27' travel trailer and pulling is never an issue. If you really want to make it interesting, a few folks make programmers for the 2.7 and it will really wake it up if you want to go that route. I have gone that direction on my daily driver and its a beast.

I have the 3.5 and tow a 27ft offshore boat. I towed it yesterday from Freeport to Tomball and got 11.5mpg. Mine is rated for 13k lbs

I used to be really sceptical of the 2.7 and towing; mainly on the durability end of things. Twenty years ago towing with a motor this small, especially turbo charged, would have eventually lead to blown head gaskets, a cracked heads, cracked cylinders, or busted pistons just from the shear cylinder pressure and detonation created to make the power with these small motors.
I tried towing one of my Rangers with just a naturally asperated Pontiac iron duke 4 cylinder in an S-10 pickup and wound up having to replace the cylinder head on it because it cracked in 11 places; all four cylinders, from the stress.
I've heard a lot of folks towing with this 2.7 and having zero issues. Even had a coworker loan his 2.7 powered F150 to his son to tow a Jeep Wrangler on a trailer to Colorado to go offroading in the mountains and it never showed any signs of weakness or giving in to the stress. They've definitley com a long ways with the engine technology.