I recommend an 8 foot bed. My wood wouldn't even fit in a 5'7 Bed lol

And wheelbase. Got lots of that

And stability...when your truck is only a few feet shorter than your camper...very stable
I just back into all parking spots and line the parking line up with the bumper. What ever doesn't fit is the parking lot liners fault.
I daily drive mine every day.
Oh oops, sorry...forgot. 1500 forum
Seriously, I find a need for every inch of bed space. But, I also do not park in a garage or go downtown much...although I have and even parallel park.
If you ar getting a quad cab the choice is made for you. Only 6'4
If your getting RamBox decision made...only 5'7
But since you are asking that means you are looking at crew cabs.
And now you have to make that decision.
The 9 inches of bed space...do you need it?
Do you need the 9 inch shorter truck?
Do you want the 9 inch longer wheelbase?
Can you live with a 2 foot larger turning radius?
And as mentioned....the 6 foot bed will weigh more.
Good luck with your choice. Neither is wrong and either will get the job down.