I like to use a red Herdim 3-sided (not quite triangular) dulcimer pick--each corner is a different thickness. Sometimes I use a triangular tortoise-celluloid Fender Med. (the thins are too flappy). When I want looser action and a "rounder" sound, I strum by one of the soundholes just north of the hollow, and it doesn't seem to mess up the fingerboard (rosewood or walnut, dep. on which dulc. I'm using). For fingerpicking, I use reinforced silk wraps on my index and middle fingernails and a thumbpick, over the strum hollow.

I don't use a thumbpick for guitar, though, except for 12-string, and then a yellow or orange Fred Kelly Slik Pik (not the Speed Pik that has that floppy little tab).