You got to first decide what kind of macro photos you will be taking.
60mm is an excellent lens. However, it lacks the working distance (minimum focusing distance at which you obtain 1:1 magnification). You might require if you want to shoot bugs. It also pose some challange in lighting the subject too because you are so close to the subject.
90mm or 105mm gives you more working distance, while 180mm or 200mm is the ultimate for bugs shooter.