I love the sound of the bare thumb but when I play with my father who is a heavy strummer it gets hard to have any volume without the thumbpick. I've tried fingerpicks and could never get used to them, I could only liken it to someone putting huge rings around the ends of my fingers and then attempt to play something intricit. It's just not going to happen with me haha.I'm a very serious fingerstyle guitarist, and I use only fingernail. I started out in classical guitar, so I guess it's only natural. I think it gives way better tone than fingerpicks or flesh.
I considered fingerpicks for a while, but then I read and interview of Leo Kottke saying years of using fingerpicks gave him severe joint pain in his fingers, and he eventually switched to using the nails on his fingers and the flesh/nail on his thumb, which is pretty much what I do now.