We recently had a split stay between SSR, in a studio, and OKW in a 1 bedroom. My two kids, 9 and 7, slept on the sofa bed.
At SSR, they complained endlessly. Their backs hurt, it wasn't squishy at all, it was too slippery for the sheets, sky is falling, etc etc. At first I figured they were just trying to scam their way into sleeping with us and they're way too big for that, but I laid on it and thought it was pretty bad... just hard and uncomfortable.
At OKW, it was more "mattress style" (instead of the weird velcro type pads at SSR) and they slept comfortably and never said a word. I also laid on it and thought it was comparable to the pullout couch we have at home, which has a good quality inflatable mattress. I probably could have slept on that one.
I think this is the last trip we will get away with not booking a 2 bedroom, though.