Hi chip,
Back pain can often take a few nights to show up and is usually an indication that either the support layers are too soft or the comfort layers are too thick and soft to provide good support for your body type or sleeping style. Without knowing the details of the mattress though it’s not really possible to use your experience as a guideline.
In terms of quality and durability they are both great and they both come in a range of firmness choices but they have a different feel so its really a preference choice with some people preferring one and some the other in either the comfort layers, the support layers, or both. The link I provided earlier in your other thread (the pros and cons of latex) talks about the differences and post #7 here has more about how they compare in terms of feel but “feel” can be very subjective and can be different for different people.
Other than that, all the materials they use are high quality but of course your own testing is the best way to decide which one is the best “fit” for your needs and preferences.
Phoenix