I like the look of unlined but lined gives me a little more confidence when playing. For me the best of both world are ghost lines where the lines are done with a darker wood that doesn’t stick out like a sore thumb compared to the fingerboard wood or partially lined where the lines don’t go all the way across the fingerboard.I have both, and generally prefer the unlined basses. I learned how to play bass on an unlined fretless, so that is where I am at home. Part of it is the look of a clean unlined fretboard, part of it is that I like the challenge of getting my intonation right without the aid of lines. That's just what I like though.