Performance, mileage, gobs of low end torque, and "fun to drive" would be the Ecoboost all the way. Especially a tuned one that can easily put out 410 hp and 530 lb-ft with spending just $450 on a custom tow tune. My tuned Ecoboost is way more fun to drive than even my tuned 2014 Cummins with no deletes. That is if you get the right tuner who knows what he is doing likeMike over at 5 Star tuning.
Any 250/2500 will handle a load better than a 150/1500 truck, that is a given. It will all depend on how much you will need to tow with it and what you are willing to deal with when towing. I can tell you that I have towed almost 10k lbs with my Ecoboost up and over the Rockies a few times and it easily pulled it at the speed limit to where I think that 6.4L might have been struggling a little bit. With the trailer loaded properly and a WDH, I felt in control of the load...well as much as you can with a bumper pull. No doubts the 2500 would have been more stable with less bounce in the back, but it was more than manageable with my F150HD especially the second time when I installed Supersprings which just about eliminated all rear end bounce. If it were me and it was between the 3.5L Ecoboost and the 6.4L then I would go for the 3.5L EB and just add Supersprings or an add-a-leaf. Now if it were between a 3.5L EB and a HD diesel then that would be a different story.
