I can only answer from my own experiences. I think, if figuring the true length of TT vs 5er, the 5er will have more livable space. Why? Because the TT A-frame (hitch) extends forward of the "box" (living are), sometimes 5 or 6 feet. At most, the king pin on a 5er extends only a foot, if not actually equal to the front of the living space.
About the upper living area. There are 3 different types of fifth wheels: High profile, Medium profile, and Low profile. The difference in these, is the height of the upper living area.
A high profile living area will have head clearance as much as 7 feet or more which allows for a LOT of storage, especially if the trailer frame is a drop frame. Sometimes, half the length of the trailer is basement area. You don't get that kind of storage in a travel trailer (although there are some being manufactured now that now have a basement the entire length of the camper.
About that front living space. Not all are the same either. Three different things can be going on in the front living space: You can have a front bedroom. And even some now have a front bath across the entire front of the upper living area. You can have a front living room, and you can have a front (full and very large) kitchen filling the entire upper area.
All three variations still afford larger pass-through space under the upper level than any travel trailer pass through with the bed in the front.
In addition, the space under the upper living area also has the front, very large cargo space directly under the over-hang. This is usually used for rough storage, fire wood, built in generators, the propane tanks, and battery banks. That space is huge and it's under the front upper living area.
Just for an FYI, I've owned 3 different travel trailers, plus a pop-up, and now a fifth wheel. I've towed bumper pull trailers all my life, and I grew up with a travel trailer my parents owned when I was kid. It was a 1963 Phoenix travel trailer and Dad towed it with a 1963 Pontiac Station Wagon. So, I've been around travel trailers all my life.
We purchased our first fifth wheel about 3 years ago. This was the first time ever I'd towed a fifth wheel. And to this day, I cannot tell or make a judgment call which one tows better. All my trailers towed and responded flawlessly for me, always.
Why? because I had the right truck with the right distribution hitch system. Even when I towed my first travel trailer (Dutchmen Sport Lite) at 24 feet long with a 1500 Chevy Suburban, it towed flawless because of the weight distribution system and the sway control I used.
When we purchased the fifth wheel, (same truck as I towed two previous trailers with), I actually liked the trailer tow better. The fifth wheel was a horrible learning experience for me. It's been over 3 years now, and now,.... it's no problem.
But, which tows better? Neither, and both. They are the same. If you have the right truck, with the right hitch system, with the right trailer, a bumper pull trailer tows just as well and just as nice, and just as stable as a fifth wheel. AND ... with a travel trailer, you do not EVER have to worry about the trailer making contact with the bed rails of the truck bed. This ACTUALLY makes towing a fifth wheel more challenging!
This are my thoughts, and my opinions based on my own experiences. You are entitled to your own opinion too.