I have 1/2" line for my mainsheet. Its too thick. It doesn't run smoothly enough when letting it out. I often have to push the boom out by hand when running downwind. Sometimes its also difficult to pull the line out of the cam cleat under load.

1/2" is overkill, although thicker line feels better in the hand, easier to pull.

I'm going to change it out to 3/8" line. You don't need very hi-tech line for the mainsheet, since a little stretch is not a problem, like it would be for a halyard.

One type of line you might want to try is "fuzzy braid" like New England Rope's Regatta Braid or Samson Trophy Braid. This has a softer feel than Sta-Set type lines. You can buy this at Sailnet or Defender for about $.53 a foot for 3/8" line.

I've heard of other sources for cheap line, "knothead rope works" via their e-bay store, "the rope dope" (Frank Lasky), or Binnacle.com. Prices are even less, but I'm not familiar with the brands they sell.