I've been using Spectra for the last 7 years. I use 20# test mostly, as the local Fisherman's Warehouse didn't have 10# in the yellow high-viz spool. I sometimes use 10# if I don't care that the line is green instead of yellow. 10# is more than enough for the 5-7 ounce 1/2A planes I normally fly. If going with one of the heavier 1/2A planes, I'd stick with 20# test, although that's overkill.
Mark