Hi Quercus,
The relative firmness of each (which I’m guessing is what you mean by support) would depend on the IFD of the polyfoam vs the spring rate of the specific type of coil you are comparing it to (which will vary by gauge, height, coil type, number of turns, coil construction, and number of coils). In some cases polyfoam could be firmer and in others it would be the other way around. Both of them can do a good job of keeping your spine in alignment depending on the specifics of the mattress design and all the rest of the layers and components.
In terms of durability … in most cases the support core of a mattress isn’t the weak link of a mattress and I would treat a good quality innerspring and a good quality polyfoam support core as approximate equals in terms of durability although again it can depend on the construction and design of the mattress and the specifics of each.
The biggest difference between them would be in terms of the feel and performance of the mattress. Innersprings are more “springy” and have a different response curve than foam. You can read a little more about some of the differences between a latex support core and an innerspring in post #2 here that would apply to some degree to polyfoam as well except polyfoam would generally be less springy, less responsive, “stiffer”, and less contouring than latex.
Polyfoam would also be less costly than an innerspring.
I think in general terms an innerspring/latex hybrid would be more of a preference issue for someone that preferred this combination in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) vs a latex support core while a polyfoam/latex hybrid would be more of a budget issue for those who were looking for a latex comfort layer but were not in the budget range of being able to use a latex support core underneath it.
Phoenix