I've used Ash for many years on fretless to help along the 'attack' of the note whereas my Roscoe Beck Fender fretted bass has an 'aged' Alder body and doesn't quite have the same attack as ash, (great recording bass though).
Thanks to Paulhauser's link here is what Roger Sadowsky says and I agree....
Ash: Hands down, the tightest, brightest and punchiest body wood.
Alder: Sweeter and warmer, with fuller midrange