I think they are equally uncomfortable. We have the U dinette and if you study the construction it's basically a standard dinette with section added on the wall end.
Ours has fairly soft foam in the cushions which is great unless you sink through it.
I'll probably change out the foam in ours to something a bit more supportive at some point.
2017 Jayco Redhawk 29XK
2015 Wrangler JKU
Blue Ox Baseplate w/Avail Tow Bar & Protect-a-Tow