ALong with in the REAL world, a TT will use more fuel hands down than a 5W, as the actual airflow up and over the truck/trailer is better with a 5W! The couple of folks that deliver rv trailers have stated that the BEST mpg is a smooth fiberglass walled non bedroom slide 5w. Airstreams are also pretty good. Next worst is an aluminum sided equal 5w, THen the front bedroom slide 5w's, then a smooth TT, than an aluminum sided TT. The TT's are typically lighter than a 5w as mentioned of a given size!
So with this, while one can argue weights need to be taken into consideration as to how well a rig will tow, design and aerodynamics ALSO needs to be taken into consideration!
With that, I have never understood the "I do not know the trailer is back there" statements. You have to, it is looking you in the rear view mirror. You put 10K lbs of trailer behind your truck, IT WILL know it is back there, as acceleration, braking in general will be slower! I do not care how big of an HP/torque motor you have, you will know it is back there!
My IHC dumptruck with a 188" wb knows it has a 12K trailer behind it! Granted a pintle hitch, that is a foot or so closer to the RA than my pickups, I know it is back there! The truck weighs 12K with over 20K of suspension!
The how well a trailer tows, will depend upon multiple items!
As to which is better......well, as pointed out, both bed and bumper style hitches have issues! I'd like some of you spouting about bed mounted 5ws try to use a dump bed of some sort to pull such a creatcher! not happening. Now a bumper pull will work.
Marty