I currently use nickel thumb and finger picks as I didn’t like the plastic ones I started with. I never really considered using a plastic thumb pick with metal finger picks until I started working on duelling banjos where I struggled on the upward strum with the metal thumb pick.
I tried the combination of metal and plastic which improved the strum but made the notes played with my thumb sound flat compared to the sound of the metal finger picks. From what I read on the web it seems people prefer a plastic thumb pick but I’m not sure why, would a better quality one (if there is such a thing) give me a better tone?