Tuckpointing: flush or concave joint?

I am about to tuckpoint my house, and am wondering what shape joint would be better. Some information I've come across suggests that for areas with mild weather use a flush joint, and for areas with harsher weather use a concave joint. But other people suggest that flush is always better as it gives better drainage. The shape of the current joint is concave, but that is not so important as it will all be done over. The climate is not mild (I live in Chicago).