I think Jeff is correct, however fretless is tougher, it requires a lot of work. If you like the sound, and I live for it, play fretless. I work on difficult stuff on fretted, then when it's really under my fingers move to fretless, the only worry then is intonation: not intonation, fingerings and everything else at the same time. This is only for academic purposes, I often do entire gigs on fretless.