ive had memory foam and also sprung with latex, both are garbage, my sprung with latex lasted the longest, at 11 months. after that the latex just sunk into itself, and created a slope that would force you off the bed.
the memory foam one lasted around a month before it would not return to its original shape.
refunds both times, although i do hear sometimes you just get a bad one, and that they are in fact great, my mate has a memory foam one, and him and his missus love it, they have haed it two years.
in the end, i went with a pocket sprung (high density) horse hair padded one that cost me an arm and a leg, but it is pure luxery.