Personally I prefer glass -feels better than steel and the tone is, to me, warmer.Never got on with a ceramic one either. You need to work out which finger you are going to use-I use third finger but some prefer to use others. I would suggest glass first from my experience-they are fairly cheap-don't spend too much cash and see how you get on. Listen to some great players like Elmore James, Duane Allman, Lowell George, Warren Haynes, Sonny Landreth, Derek Trucks , Ry Cooder and many many more than I can't think of right now.Can I suggest Fretboard Roadmaps blues edition will get you going too and bear in mind that you can use different tunings -I think that string damping is one of the most important elements of playing slide. I play mostly in standard tuning though as I use the guitar for a 2.5 hour set and don't like having to mess with the tuning but at home I have an acoustic open tuned in G. Sorry,I have prattled on.