Hi Brototype,
The density of memory foam or polyfoam is the most important factor in its quality/durability but with latex density is a comfort spec not a quality spec and knowing the density is unimportant. The way to compare latex is based on the type and blend of the latex (see this page). There is more about the different types and blends of latex in post #6 here but the 10" Ultimate Dreams latex hybrid uses blended Talalay latex in the comfort layers which is a high quality and durable material.
The choice between latex and memory foam would be based on preference because they are very different materials. There is more about how they compare in post #2 here but the best way to know which one you tend to prefer would be based on your own local testing and personal experience.
Phoenix