I have always used both pick and fingers, depending on a variety of factors. I love playing my Rics with pick and roundwounds with some drive (or lots!). I've been playing my recently-Alembicized short scale Guild M-85 with fingers almost exclusively, but it's fun with a pick too. My 5-string Alembic with my improv soul-jazz band is 75% fingers/25% pick.
I play very differently with pick, though sometimes I just try and play things both ways, even if it would seem "obvious" that it's one or the other. I think actually a lot of the classic stuff was played with pick, like if Joe Osborn or Carol Kaye played on it. I remember playing along with Blues Traveller stuff with the fast finger stuff but with a pick - it's a challenge, especially to make it sound good, but it's possible. Or Tower of Power or James Brown too. At a gig I'd probably go with fingers to try and catch the original vibe but nothing to stop me from messing around during practice.
Here's something I would never have come up with without a pick and my Ric 4001: