I switch around to different thumbpicks all the time. (I get bored easily. *G*) Varies from Kelly speed picks, to Hercos, to Ernie Balls (my favourite) as well as Golden Gates. They should fit snuggly but not so tight that it's cutting off the circulation in your thumb. The more aggressively you pick, the better the chance the thumbpick will start slipping and sliding around and your fingerpick does sweat in there as well so nice and snug is the ticket for aggressive/hard picking and something a little looser fitting for softer, lighter picking.