just try em all and see which suits you i like the tow haul feature but sometimes it will downshift too much when u get on the brakes hard and result in some crazy 6000+ rpm engine revs. manual is great if u want to fool with it
I use tow/haul mode in the city and when in traffic. But go to just regular when on the highway, sometimes if it is hilly I will lock out 6th gear too. I never use the M mode, seems to be to much work while towing, that's why I got the automatic, the computer is very smart.
The majority of my towing could probably be done with an F-150, so I'm not really working the truck hard at all. T/H works fine for me.
Using T/H at the last Ohio meet (15k lb trailer) the thing would not get out of first gear with the throttle pegged while going uphill. This last trip, pulling 16,500lbs on the same hill wide open, I used M and popped it into 2nd around 5500-6k rpm. No problem whatsoever, my timing and speed was much better in this case since I had full control over it, but this type of towing is a rare circumstance for me (annually at this point).
Since the truck is new to you, I'd leave it in T/H while you get used to how the truck reacts pulling the trailer. Let the truck do the thinking!
Just finished up my first tow with my new truck.... about 8500# bumper pull over and through many mountains on an 800 mile trip. I found that DRIVE with the T/H button depressed worked really good with two exceptions. Running up a hill, the computer is too aggressive IMO and would rather run the rig at 4500-5000 RPM to keep the speed (cruise on) than to adjust five MPH slower and keep a more desirable gear and RPM for the grade (~ 3000 RPM).
I played a bunch with the M mode and found it, as others have chimed in, too much trouble for normal driving, but.... on an extreme grade, using the M mode made life much more enjoyable and It was the only stretch of my trip that I thought a diesel would have been a better choice. These new motors are pretty good pullers!