Ceramic. They're quieter than semi-metallic and not as hard on rotors. The downside is that they're generally more expensive. But you're not likely to be replacing rotors very often with ceramics, so in the long run they're really cheaper.
curmudgeon: noun; a crusty, ill-tempered, irascible, cantankerous old person . . . .
79 27' Holiday Rambler Statesman, 78 32' HR Imperial, 85 36' HR Imperial 5th Wheel