'Best' depends on the situation.
5th is superior from a stability and maneuverability standpoint, but puts a lot more weight on the tow vehicle, meaning you generally need a larger truck for a given trailer weight. This configuration also gives you more trailer space for a given overall rig length.
TT is better if you are close to the payload limits of your tow vehicle, want the extra storage space, or want to tow with something other than a pickup. They aren't as stable as a 5th, but are perfectly usable in typical situations when properly configured.