Although they may offer differences in sound, the popular belief being that rosewood is warmer whilst maple is brighter, I think these characteristics are overstated in so much as the fretboard wood alone will not change the sound a bass produces significantly (at least no more than any other part). If there is a change it also depends on the individual example of wood and I should imagine generalisations over an entire species may only give a rough idea at best. I wouldn't bank on the fretboard imbuing your bass with any predictable, distinct tonal characteristics.
Because of this, I would choose a fretboard firstly upon looks and feel, something which is particular to each person.
The only disadvantages would be if you were playing a fretless as maple, I believe (although please correct should I be wrong), get's chewed up more by strings unless it is given a very hard finish - something not everybody likes. Again, I would be hard put to come with any objective advantages or disadvantages with either of these woods; it's very much up to you.
Many people will disagree with me I'm sure, and as always, this topic has been covered a lot in the past, so it's worth doing a search. I'm sure you'll find comments from those more emminent, experienced or otherwise more qualified than me.
As always, YMMV and IMOs and IMEs apply were necessary.