Based on sales, for flippin'/pitchin' style jigs it's about 60% 1/2oz, 30% 3/8oz, and 10% for the rest. On football heads, it's closer to 50% 1/2oz, 40% 3/4oz, and 10% for the rest. Those are estimates, but I'd wager they're pretty darned close. The trend is lopsided waaay more toward heavy heads than lighter.
If you had to use just one weight, 1/2oz is the way to go. Let the terrain/cover be your guide as far as the head style goes.
