IF you plan on towing, then the 3.5L Ecoboost will do a great job towing. the truck is lighter, and can carry more because of that. If you get the longbed, and Max Tow packages, along with making sure it has the maximum GVWR, you will have a great truck that is lighter than the F-250 and can out tow with it too!
You no longer need to have the '4.10 rear axle' because of the new 6 speed transmissions. The 4.10 rear axle did not get good mileage anyway, the engine spins to fast while driving at freeway speeds.
You might consider a 2011 - 2012, as they have good tow ratings too, but it is difficult to know if it has the 'tow package' without looking up the GVWR. The GVWR is posted on the drivers door - of course. The 2015 aluminum body F-150 had a 700 pound lighter weight advantage to the used F-150's.
My boss just bought a 2014 F-150 and I was telling him to get a 2015 with the 2.7L Ecoboost. He had no plans on towing anything, and it would use about $500 less a year in fuel - compared to his 2014 F-150 that has a higher curb weight, and 3.5L Ecoboost. I guess he wanted the higher HP 3.5L and did not care about the lower mileage. He also got a great rebate when he bought it in December.
If you just go to the Ford dealer, and take the 'pretty blue one' that you see parked in front, it probably will not have the required towing package, or higher GVWR that you might want to tow your trailer, or perhaps a larger trailer someday.
And the 2004 and earlier F-250's did not have much of a cargo rating, compared to the 2005 and later with a 10,000 GVWR. The SRW F-350 went from pre 2004 9,900 pounds to 11,400 pounds (give or take some weight rating) after 2005. So all trucks have improved over the years!
Good luck,
Fred.