John at Traditional Boat Supplies sent me some samples of his Polyhemp rope which I liked the look of: tradboats.com
and I've also had good service from Pete Flockhart at Tradline Ropes and Fenders: tradline.co.uk who stocks both polyester and polypropyene 'hemp effect' ropes, both 3 strand and also braided which is ideal for sheets etc.
Probably the best thing is to request some samples and compare prices. I do know that the original polypropylene 'hemp' ropes didn't always wear well, so my inclination would be towards polyester. But the price difference may well be an issue.
I'll be re-rigging my own boat this year, so I'm interested to see what other recommendations are made.