I have had good luck with GM but I am a GM guy, as does our company. We have ran ford and gm vehicles and are currently almost all gm now for different reasons. On our GM vehicles the 5.3 lasts but can give you trouble with the DOD (displacement on demand) or 4 cyl. mode with stuck lifters. If caught right away you can repair the lifters and keep on going. Fords have also had issues with timing chains and other valve train issues.
Both have their pros and cons, and you can hear equal amounts of horror stories on either. And once you ask which one is more reliable that’s when you get the biased reviews typically.
If this is just a tow rig I would opt for finding something with 4.10 gears or 3.73 gearing at least. It will hurt mileage but if you are just towing Id rather have the right combo and pay more at the pump.