Hi Supravista,
It depends on which mattress/topper combination provides you with the best PPP (Posture and alignment, Pressure relief, and Personal preferences) on a specific mattress for a specific person and personal preferences are only one of the “P’s”. You may “like” the subjective “feel” of a certain topper but the combination of the topper, your mattress, and you may still not provide you with the Support/Alignment or Comfort/Pressure relief you “need” (these are “needs” not “preferences”).
There are hundreds of different versions of memory foam and each individual supplier will be more familiar with their own products and how they compares to each other and the other types of memory foam in the market than anyone else(there is more about the differences between different types of memory foams in post #9 here and post #8 here).
I’m happy to help with “how” to choose but the specifics of “what” to choose will depend on all the many variables that are involved and there isn’t a formula or “theory at a distance” than can predict the best choice for you with any certainty.
You can compare the “quality/durability” of a product based on its type and density but that has little to do with the feel and performance of a specific type of memory foam and outside of the guidelines I linked, a conversation with an experienced and knowledgeable online retailer or manufacturer that has your best interests at heart and that can give you good information about what they sell is your best source of guidance. If you are still uncertain after that then their return or exchange policy may also be an important part of your personal value equation. Each person can be very different and what works perfectly for one person may now work well at all for another with a different set of circumstances, needs, or preferences.
While it’s a common belief with consumers that there is a “formula” that can predict the “best” choice with some certainty … there are just too many variables and unknowns for this to be possible and the knowledge and experience of a manufacturer along with their return or exchange policies can be among the most important parts of a successful topper purchase. Once you know how to eliminate the worst choices or the choices that are most likely to be unsuitable for you and you know how to make meaningful comparisons in terms of quality/durability … then only you can decide on which choice is “best for you”.
Outside of the members here (which jankc suggested and which I specifically recommend) … the previous link I included in my last reply with the topper guidelines also links to a list of some of the better online topper sources I’m aware of.
Phoenix