Hi Padinn,
This would really be a preference choice and it would really depend on how you feel about the feel and fast response of latex vs the feel and slow response of memory foam. Latex has a more “on the mattress” feel and memory foam has a more “in the mattress” feel. Latex is more resilient and motion friendly while memory foam is less resilient and a little more motion restrictive.Some local testing on mattresses that use both types of materials in the top layer could help you get a sense of the difference for yourself.
Latex will be more durable than 4 lb gel memory foam and will also be a little cooler but there are many elements to what makes a mattress sleep warmer or cooler besides just the foam that is used on top (see post #2 here) and they have a cumulative effect.
With latex there is also a choice of softness levels while with memory foam you only have one.
Hope this helps.
Phoenix