[Nonfractal]

Jeremy, 
I've only used grub screw fitted pinions once and didn't find any advantage in them. 

I've used slot-it Ergal, NSR brass and AllSlot steel pinions and really dont see any difference in them. 
The wear on a pinion seems to be on the friction fit surface ( as it gets fitted and removed ) rather than the tooth face.

I've never been a fan of nylon pinions and avoided them for the longest time. 
The Ninco angled  ones were particularly bad. 
However, when Giovanni released the ThunderSlot Lola, it came pre fitted with a nylon pinion so I gave it a go.
The thunderslot drive train is very good. I've bot had any reason to complain apart from the selection of available gear ratios. 

For me, the materials come second place to "size and fit" when selecting gears. 
Modern manufacture and materials are really quite good.
Alan