You can spend more, but we've had great experience and longevity with halyards of 12-strand dyneema/spectra. The old ones had a cover spliced over the winch/clutch area. Just before the NA's we noticed wear near the splices on two and replaced them. Samson Warpspeed (5/16 inch for Jib, 3/8 inch for main) stripped from the mast exit up with luggage tag splices for the shackle. We've never noticed any problem with creep. Higher tech lines than these can be sized so small they won't hold in your clutches or you have to clutch and cleat as we do. Polyester double braid is fine for main because it must be flexible and easy to handle. We use those gold dock lines you see on big power boats for genoa sheets. Don't laugh; they're fat, fuzzy, and cheap. The fatter the better, easy to handle, great on the winch. Only the last three feet get loaded up anyway. Extra long so they can reach the winch, even over the pole. Still usable if you have to cut off a couple feet after a bad wrap.
When it's light we use extra skinny spectra spin sheets. Our primaries are too fat and heavy with big doughnuts and old style snap shackles. I'd like to get something with a wider range, smaller in diameter, still flexible and easy on the hands. Also better, lighter shackles that don't come off when you wipe out during a jibe in heavy air...which leads to shrimping, a torn spinnaker, and loss of four places at the NA's, oh yeah, did that!
