Ebony. Maple is a close 2nd. I only buy rosewood if it's such an awesome bass I can't live without it. I kinda dislike rosewood. Too soft for a proper fretless, tone too dull.
^This
Rosewood is actually harder than maple.
Rosewood is indeed harder, but being a naturally oily wood it dampens the tone a tad. Not that this makes it inferior, we all like different levels of brightness.
