Hi daphnep,
Both of these mattresses have lots of feedback on the forum (the Ultra Plush more than the gel foam model) and a search on Ultimate Dreams will bring up many posts about them.
Dreamfoam is a recommended member of this site which is by invitation only and means that I believe they are among the best quality/value available in the country.
They are very different mattresses because latex is a very different material than memory foam and the choice between them would depend on your preference between slow response gel memory foam materials and fast response latex. Both are great value if you are comfortable of the risk of an online purchase with no refunds and the Ultra Plush has the benefit of being able to choose your comfort layer (they are good at prviding guidance about the best choice). They also have latex models (either all latex or latex over polyfoam) where the comfort layer can be exchanged for a softer or firmer version at a low cost if you find you would prefer something either softer or firmer than the original choice you make.
There is also a list of some of the better options in the Los Angeles area in post #2 here which has some great quality/value choices in a wide range of different materials. In general it’s a good idea to test different materials locally to get a better sense of the types of mattresses and materials that you prefer before making an online purchase. It is also less risky to buy a mattress that you have tested for PPP in person (Pressure relief, Posture and alignment, and Personal preferences) but even if you do decide to go with an online purchase the risk can be reduced if you have a better sense of what you need and prefer from local testing of mattresses that use similar materials.
This thread has a comparison of the relative risks and benefits of ordering online vs a local purchase that may be helpful in deciding on which would be best for you.
Phoenix