Steve gave his answer but I'll add another data point.
I always knew I wanted to play fretless - I did play cello in grade school ( a l-o-n-g time ago...).
My wife suggested I try a fretted bass first, which was not a bad suggestion, as it did minimise startup frustration probably.
Played that for 3 months and bought a fretless. Both 5's. Sold the fretless back to the guy I bought it from - he really wanted it back and while I really liked it too, by that time I had played a Roscoe so the hook was set. Bought the Roscoe fretless 6 and haven't really touched anything else since.
Steve is right on the versatility, which is mentioned in many threads here. There's the pantheon of "stupid fretless tricks" which fretted basses just can't do - or only with great difficulty. But if you concentrate on developing accuracy and intonation, there is no reason why anyone would necessarily suspect you're playing fretless, although they may sense that you are more expressive than a 'normal' bass. You can do things like sweeten certain intervals (especially 3rds) that fretted instruments just can't. You can also sound like doggy-poo if you get lost above the 12th fret, thank you for not asking how I know.
Now, my fretlesses are unlined, so almost everybody knows -something- is up just by looking. This is a much more subtle distinction with a lined fretless, which is the subject of many stupid borderline-religious arguments here on TB. My position is: I know what I like and I don't care what you like...
Perhaps emboldened by my fretless experience, I have recently acquired an electric upright, which fits well with my jazz and bluegrass direction. The Roscoe will probably be semi-reserved for blues and blues-rock and yes, I have had people tell me "there's no fretless in rock & roll." And "Blues Police" tell me there's no such thing as 6-strings in blues. Ask me if I care ;-)...
)
When I first went from my 3006 to a 3005 I strung mine with a high C but nowadays I use the B quite a bit more than I would use a C.
