Originally Posted by M_S
Disc brakes have more stopping power, and are better in the rain, they are also heavier, but that shouldn't make too much difference for commuting purposes. They are also bling to attract thieves, so don't get them if you don't need them.
I agree with the rain part, but if a brake can lock the wheel, then it has as much braking power as any other brake that can lock the wheel. Brake modulation is the key factor.