Hi tatanka,
Unfortunately I wouldn’t consider either of your choices to be good value.
A mattress is only as good as its construction and the quality of the materials that is inside it. Without knowing the specific details of the layers in a mattress … it’s not possible to know its quality/durability or identify any weak links in the mattress. You can’t “feel” quality in a showroom but it will have a significant effect on how long the comfort and support of your mattress will last. As you can see in post #2 here which talks about the factors involved in the durability of a mattress … all foam will go through 3 stages of softening and only the final breakdown of the material (when it forms unweighted impressions) is covered by warranty and then only if the impressions are deeper than the warranty exclusion. Unfortunately … the gradual (or rapid) softening and breakdown of lower quality materials and the loss of comfort and support that goes with it is the main reason a mattress will need to be replaced and this is not considered to be a manufacturing defect (it’s what lower quality foam always does) and is not covered by warranty.
You can see some comments about the Prana here which reflects the same concerns that you have already read about. A forum search on “Prana” (you can just click this) will bring up more comments as well. If they have “fixed” this (which is a claim I would treat with great caution) … then they should be able to validate this by disclosing the specifics of the foam layers in their current models including the density of the upper layers of polyfoam which I believe are still there.
You can see an analysis of much of the iComfort lineup including the Renewal Refined in post #11 here. As you can see … this specific model only has an inch of low quality/density foam in the upper layers (the 1.3 lb “support” polyfoam) which is inside the minimum that I would usually suggest in comfort layers (thinner layers of low quality foam will have less effect on the loss of comfort and support as they soften) but based on the quality of materials in the mattress and its design … it is not good value either (like all the largest major brands) compared to other mattresses that use higher quality materials and sell for lower prices.
I certainly wouldn’t want to be choosing between them because you are choosing between two mattresses that I normally wouldn’t consider at all in quality/value terms … regardless of how they may feel in a showroom when they are new.
So I would want to know the specifics of the Prana layers so you could compare the amount of lower quality materials in each and make a more informed decision. 120 days is not enough to know the durability of a mattress although it does at least cover the break-in period of more rapid initial foam softening which is followed by more gradual softening over time (with lower quality materials softening and breaking down more and faster than higher quality materials).
Phoenix