I read an interview with Jim Dunlop (in 2008), where he explained
I have the opportunity to work with the greatest guitar players of our time. Like I said, I equate what I do to making paintbrushes for artists, and there’s brushes for different strokes, and brushes for different landscapes, and you’ve got a fine brush, and you’ve got a wide brush… picks are the same way. You know, if you want a different tone, it starts with the pick. If you use a metallic pick, you’re going to interact with the strings differently; it’s going to be very bright, like a harsh sound. If you go for a celluloid pick, it’s going to be a soft tone. It’s a very soft pick, and it’s going to give you a more mellow tone.
I’m sure that what he’s saying is true, but I’m done, I’ve (somewhat arbitrarily) picked the 2.0mm Flow as my pick.