An aside that has nowt to do with thumb picks: I find that depending on the 'sound' I want from my old D-28, that the thickness of the pick is crucial. Also, I sometimes use one of the more rounded corners instead of the pointier one. It also makes a big difference as to where one strikes/strums the strings--near the bridge, over the sound hole, etc. I'm partial to Fender picks, but when I can't find any of the two dozen or so I leave around, a piece of plastic/folded match book cover sometimes has to do.