Fingers (and thumb) ever since I started playing some 30-odd years ago, at least until a few months ago that is, when I joined a Jam/Weller tribute band and had to get my pick-playing chops up to speed sharpish!
It's actually been a good discipline to learn, much like bowing has improved my upright playing, and has made me appreciate it as another valuable string to the bass player's bow. Finding the right gauge pick for me was vital (0.8mm, since you ask).
Cheers
Gareth