11 to 52 on accoustic, 9 to 48 on electric. The heavier you go, the better the sound, but you get less sustain and more work than with lights. I used to know a pro jazz guitarist who used 16 to 64 on a Les Paul to get the fattest sound available. The old jazzers used to use these sort of gauges on arch tops for volume, but they used to tune them right down to C to reduce stress - this also facilitates playing in the flat keys preferred by the horn section. For resonator guitars, my memory says that Dobro used to recommend lights if you didn't have a spider, and mediums if you did have a spider.