Hi Djmesh,
Welcome to the Mattress Forum! 
In order to evaluate a mattress and properly compare it against your other choices, you would need to find out the information listed here about the type and quality of the materials in any mattress you were considering. If you can find out the current specifications for these two mattresses and post them back here I’ll be happy to provide some commentary on them for you.
Being in a higher BMI range, it would be important to make sure that the materials you investigate and more durable and appropriate for your needs. Post #3 here has more information and suggestions about heavier weights that is worth reading. A high BMI presents special challenges and generally requires firmer materials (in the support layers especially). This could be firmer latex or innersprings (the type of support component would be a personal preference and in the right design either could be suitable) or even a zoned construction. The same overall guidelines apply with higher weights though that PPP (Posture and alignment, Pressure relief, and Personal preferences) along with using high quality durable materials that will maintain their feel and performance for longer periods of time are the way to make the best choices. Heavier people in general will need firmer and thicker comfort layers and firmer support layers than those who are lighter and because no materials will last as long with much higher weights the quality and durability of the materials and components is even more important than normal. I wouldn’t “rule out” any types of mattress and base your choices on your own personal testing.
You’d want to get that information at the retail store you visited. If you’re not able to go back, I would phone them and ask for the specifications from your visit.
Without having complete specifications, again you can’t begin to make meaningful comparisons. While price is certainly important of course, the “value” of a mattress purchase is what is most important and price is just one of many factors that can affect the “value” of a mattress purchase. There isn’t a “formula” that can be used to assess or “calculate” the value of a mattress because there are so many different variables and criteria involved that can affect the price of a mattress that can each be more or less important to some people and not to others who may have completely different criteria or definitions of “value”. The value of a mattress purchase is also relative to how a mattress compares to the other finalists you are considering or to other mattresses that are available to you in your area (or online if you are also considering online options). There are many reasons that a mattress that may be “good value” for one person or in one area of the country may not be good value for someone else that has very different needs and preferences or that lives in a different area.
There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
I’ll look forward to your reply and hopefully with that information I can help provide you more accurate and detailed information that you may use to further refine your mattress shopping process.
Phoenix