There's really not a lot to choose among the two for image quality. They're both superb lenses for sharpness. The main differences are:
- EF vs. EF-S (60 can't be used on a full frame body like the 5D).
- Focal length/working distance (60mm hard to use on living subjects, but can be used with slightly slower shutter speeds, making handholding easier).
- Physical size (the 100 is bigger lens than the 60; about twice the weight).
Otherwise, cost and quality-wise they're very similar. As NaturesPixel says, if you're planning on going for bug macros, the 100 is probably a better bet. If you're going for tabletop macros and handheld then the 60 has the edge.