All my Gibson fretless basses sound fine, maho is as good a combination with fretless as maple or alder. But my fretless Grabber, which is most likely an aftermarket conversion, sounds raunchiest, spluttering tone all over.
That said, I don't know yet how my natural Les Paul Money Bass will turn out whom I'm having convertet to fretless as we speak.
As regards choice of boards, I probably have a slight preference of rosewood over ebony for the more pronounced mids, I've never played a fretless maple board though I'd like to try one.
I also have a P Bass sixties reissue from the eighties in fiesta red with an aftermarket rosewood extra-thick fretless board and that sounds awesome as well. A lot of good fretted instruments have an excellent fretless "sleeping" in them.
Uwe