Both! Really nice doggie ortho beds come with a layer of egg crate foam AND memory foam. The memory foam will compress causing the dog's body to sink the the floor anyway. The egg crate foam won't compress as much and provides support for the memory foam. When used in conjunction with each other, you get very good support and you don't have the heat issue with the foam.
I bought both my crate pads at Petco. The blue one is newer and is memory foam. The brown one is the egg crate foam. Since taking this picture, I've reversed them so the egg crate foam pad is on top. She REALLY likes them now.
C-ATCH Pimg - DOB: 2/06, RATO, UJJ (x2), DJA, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014
RATCHX High Jinks vom Neuanfang - DOB 9/12 (Gotchya Day: 1/23/2013) CA, agility superstar in training