Also length; over about 35 feet line length, polyester arguably stretches too much. That said, Dyneema also needs to be stronger (and the mountings) because the forces are higher. I think the obvious answer is that one-size cannot fit all. (edit--I just saw Jackdaw's post. There you go.)...Location of the jacklines is also a consideration.
To me one of the greatest considerations is UV resistance. I have always (multiple boats) left jacklines rigged full-time, since I never know when I will need them and I single hand most of the time. In that case, even polyester webbing doesn't last long.
Finally, try to keep them away from under foot. Many boats can run them along cabin sides or similar. Not always.