Lighter gauge strings are good for a more expressive tone on fretless. Heavier gauge for more thump and less mwah. Setup is also a critical factor in generating the tone you're looking for, much more so on a fretless than a fretted IMO. I'm no expert, just learning as I go by trying things out and finding what suits me. Be interesting to see what the fretless gurus of BC have to say!