At one point I thought about the Polymer tantalums because they have a benign failure mode compared to their Solid Tantalum cousins, but alas, they are just too expensive for me. Plus, I can get lower ESR using OS CON caps, and for those who care, they look stock too.
In terms of solderability, the solid and polymer tantalums win because there aren't any plastic parts you need to worry about melting, and the part you solder is bigger too. So if I didn't care about money or ESR, then yes, polymer tantalums would be the way to go.
Does lower ESR than polymer tantalum matter on something like an SE/30 motherboard? Not really, no, especially not on a stock motherboard. Maybe a tiny bit with everything maxed out and accelerated to the hilt. ESR on those boards is about supply quick amounts of current when needed.
Where ESR does matter is on the LC575 motherboard, especially when overclocking to 50MHz or beyond. My friend Kay Koba told me his solid tantalums (which have higher ESR than polymer tantalums) wouldn't overclock to 50MHz in the past, but when he heard about me using OS CONs, he swapped out his tants for that and then could overclock to 50MHz. So it probably was a matter of that fast and power hungry 040 CPU needing more current, or perhaps being more sensitive to transient voltage dips, which the lower ESR OS CONs could supply.