I've had all 3 beds, 5.5, 6.5 and 8'. The 6.5 is the best compromise. I currently have an 8' bed and if I ever get another truck 1/2 ton or 3/4 ton it won't have anything less than 6.5.
When I had my F150 super crew with the 5.5 box it was always a PITA to get lumber. If I wanted anything over 12' I had to take my utility trailer. Loading up camping gear with a TT I always had the rear of the truck completely full since TTs generally have little exterior storage space.
I have a CC LB now and park where ever I want. It may take an extra maneuver but so what. Only downside is it take a few minutes longer to wash. :)