Pick and fingers. I also vary the slides. Sometimes I use a Coricidin bottle on my ring finger, sometimes my small finger. I use a brass slide if I'm playing a National. The sound of glass is more smooth and sweet.
Steel is a good compromise and socket wrenches are ideal.
They're fantastic, but you really need very heavy strings. And if you're playing more than a couple of numbers, they do wear your small finger down, and you don't want to be tiring your hand. I can cope with both. We went back after the last American tour in '85 and just got stuck in Europe touring and recording. We were trying to sort out the right record deal, and I don't know where the years went.