Hi Bubbly,
There are too many unknowns, variables, and individual sensitivities involved to be able to predict which mattress would be best for any particular person based on “specs” or "theory at a distance (see post # here) and the only reliable way to know will be based on your own sleeping experience. Hopefully you had the chance to do some careful and objective testing on both mattresses using the testing guidelines in the tutorial post which would give you the highest odds or predicting which mattress would have the best chance of working well for you.
A mattress that keeps you in good alignment and provides you with good pressure relief in all your sleeping positions is always the mattress that is best for any particular person but there are so many differences between people that there is no such thing as a mattress that is “good for backs” in general … only a mattress that is best for “your back”.
While none of the mattresses you are considering use particularly high quality materials … I would also keep in mind that it’s much easier to “fine tune” a mattress that is too firm by adding a softer topper (see post #2 here) than it is to try and make a mattress that is too soft any firmer or more “supportive” (outside of some temporary or partial improvement) because this would generally involve removing comfort layers that are too thick or soft or a support core that is too soft (see post #4 here) so I would tend to make sure that if you are uncertain that you err on the side of a little firmer rather than softer because your options to do any fine tuning would be better if the mattress you are exchanging for doesn’t turn out as well as you hope.
Phoenix