Ideal line for Aries
 

Simple enough... What would be an ideal line for Aries windvane tiller lines? No larger than 5/16", for running around several small sheaves, low-stretch, holds a stopper knot well, and abrasion-resistant (as the nips would be infrequently freshened). Given how little of the stuff one requires, even counting spares, it could be a high-tech (read: expensive) line, and still not break the bank.
Any suggestions?

I have had great success since '80 using polyester coated kevlar line. I've used knots as well as Brion's methods of stitching to form and eye (for topping lifts and other applications without having to splice). A more modern version is; Krypton-T Double Braid (100% TECHNORAÆ Core).

There's no point in going with the more exotic HM line combinations for your application.

HM Blend Single Braid
 

I'll preface this with the fact that I have little experience with windvanes, but lots of experience with small tackle systems and experimentation with different types of rope.

I have had good experience with the single braid HM blended ropes -- the original was Maffioli SwiftCord, but there are several others out now. These ropes are strong, inelastic, and run nicely through blocks. Pricing is sort of medium.

Eyesplicing these can be tough - there is not a lot of interior room for tucking -- but they do hold knots fairly well. I have good luck with multiple brummels as well.

Bob