for me the sound doesent mater so much between ebony and rosewood, but rosewood has a warmer tone and the ebony is a bit like maple, almost the same tone!
i prefer rosewood for a fingerboard, because of that soft feel (the grains are more present) on the rosewood.
ebony is more hatder i wouldnt say faster because all the "fast metal guitars" has rosewood fingerboards (ibanez, jackson, esp) almost all of their guitars has rosewood fingerboards! so for me ebony is NOT faster, it just has a very different feel form rosewood...but taste is very important, try them both for a some time, then you will see the differences and the ones that you like... -cheers!!!