The best fretless playing I have ever heard was Alain Caron, in Mike Stern's quartet. His F-Bass tone was gorgeous, his pocket playing flawless, but best of all was his soloing... one of them was so damned melodic, the tune actually got stuck in my head and I found myself whistling it next day. Playing a machine-gun flurry of notes and calling it a solo is all very well, but it takes a [i]real[/i] musician to make it tuneful, and he did it in spades.