@xines
Could go either way. I've owned both, and honestly I've mostly gone by
"whichever's cheaper for equal or better comfort at the time I need to buy a new one"
You can have a terrible futon, but you can have a terrible mattress too. The things to watch out for, like other beds, are the thickness and materials. Most futons are sold without any sort of support beyond "wooden frame you can fold up into a couch" (over the years it'll lump up if you don't rotate it once in a while from doing this), so they can be a bit lacking. But then they can be a whole lot cheaper too and if you like something firm for sleeping on, it won't let you down.
My current bed has a futon mattress atop the box-springs and frame legs that were still perfectly serviceable, as that was on sale. I might try to repeat this particular combination when I replace it in a few years once again, it's been rather nice.