IMHO, it really depends on whether you will ever actually use it as a bed. If you do, will it be for children or adults? If you will rarely use it as a bed, and it'll be children, I'd say the J-Steel is fine. If you plan to have adults sleeping on it often, I would say try for the hide-a-bed. I didn't notice any difference between sitting in the J-Steel vs the hide-a-bed.
I can't speak to the sleeping comfort of the Denver Mattress in the Hide-a-bed, but having opened ours up a handful of times, it resembles a very firm foam mattress, not memory foam, just foam. Also, there are a lot of joints and crevices when it's folded out, so you'd want to put something over it more than just a sheet to smooth things out a bit.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!