I use 5/16" Samson Trophy Braid for my mainsheet. It's an inexpensive polyester double-braid with a fuzzy cover that is soft and easy to grip. It's stretchier than the dyneema blend lines, but I don't think that matters. A hand-tensioned sheet simply doesn't take enough load to show significant elastic elongation.

The biggest downside to Trophy Braid is that (being polyester) it absorbs water. So, when fully wet, it might add (probably less than) a pound to the weight of the boat. For me, that's not a big deal.