I would test drive them all, see which one is the most comfortable. For 90% of driver's towing the difference to getting to the campground is minimal.
On paper the Hemi 6.4 is supposed to be the strongest, but the Ike Gauntlet exposed an issue with what people suspect is the transmission gearing in the first 1-3 gears. However not everyone is going to be driving at 9,000'-13,000' at wide open throttle.
The 6.0 has been around for a long time, lot of support for them etc. I had the 2008 Chevy 6.0 and it's plenty strong for most.
Just go test drive em and go with the truck you like the most for the money your going to spend.