ORIGINAL: MikeSell
If all you are interested in is unbreakability choose those soft props. I like performance from my planes. You get the most performance from props that don't de-pitch when in use. I did extensive thrust testing and I like the Graupner and the Cox grays the best. I wish Bolly was still making props; nothing I ever tried beat theirs.
Thrust testing will tell you which prop is best to pull your workbench around the shop.
In real world duty, the rubber props will get the job done. The course record for 1/2A pylon at a local club that has been racing for over 25 years is held by a 5x3 rubber ducky Cox prop.
Every other commercially available prop [and a few others] that are known to man have been tried there and the lowly rubber 5x3 Cox prop rules the roost.