I've been sort of experimenting for the past 6 months. Sometimes, I'm in the mood to fingerpick quietly and use only bare fingers; other times I'll use just bare fingers with a bit of nail and a thumbpick but here I use different thumbpicks all the time. Seems to vary from regular white Nationals, to a very thin, slim and light version of the National, and also this other thumbpick that's kind of strange looking but is extremely useful.
It looks just like a flat pick but has a rounded attachment that allows it to slide onto your thumb...so you can instanty switch back and forth from fingerpicking to straight flat picking a run. It's like wearing a flat pick.
When I do use fingerpicks (not often) I either use metal Nationals, or plastic Alaska Piks. The Alaskas are more comfortable but not as loud, but you feel more in contact with the guitar...For sheer volume, nothing beats the National metal finger picks.