What Duke doesn't mention in his good advice above (but appears to assume) is that it prevents the wrong ammo problems when you set up separate squads for ranged weapons that use different ammo types (arrows vs bolts vs javelins, etc.) I have tended to specialize in one weapon type for my fortresses also and just sell off the other types or melt them down.
I tended to bows for a while, but in general I pick one for a fortress, doesn't matter to me so much which. I might let a good immigrant with high skill in one type decide my choice, let him play military "hunter" a while, then set him up as squad leader and trainer.