Dinolp is the brand I prefer. I use the pick mostly for travis picking.
The sound that I get out these picks is just what I want. Not too hard nor too soft.
One interesting fact: I usually use a dunlop medium size pick, but I ordered by mistake one size large pick, and the pick is still a very good fit, I have small hands, so I was a little bit surprised that the L sized pick fitted my thumb so well.
As far as thumb picks go in general, you have to try your way out, and that way find the one that is the best pick for you.