John Wetton (post-Crimson), Tony Levin (sometimes), Michael Anthony (sometimes), Greg Lake...
I'm about 60/40 pick VS fingers.
I "discovered" flats in the early 2000s when I was recording at a studio owned by a session bass player/jingle guy. He saw my Ric and mentioned how much he loves the way they sound with flats. Gave it a try and loved it. Great for certain things, especially with a pick. I'll always be a round wound guy, but I currently have 2 of my basses strung with flats. Ironically, they're my Chris Squire Ric and Geddy Lee Jazz.