When it comes to macro lenses, two of the things you need to take into account is Depth of Field and Field of View. With a 60mm lens, you are going to have a greater FOV and less flexibility in terms of DOF. You'll need to get pretty close with a 60mm to do either macro photography of insects, or for portraits (unless you want the wider field for your portraits, and are not interested in getting close-up facial shots.)

On the other hand, with a 100mm macro lens, you are going to have a narrower FOV, and greater flexibility in terms of DOF due to the longer focal length. You won't need to get as close to snap shots of either insects or close up portraits.

In terms of build and construction, hands down the Canon 100mm f/2.8 Macro lens is one of their best-built lenses. It is solid, and has some of the smoothest focus I've ever encountered. Its clarity and quality are second to none. One thing you should be aware of, however, is the difference in these two lenses mounts. The 100mm is an EF lens, designed for full-frame sensors. It will work on an APS-C, however it will effectively be a 160mm lens. The 60mm is an EF-S lens, and is designed to work only on APS-C sensors. It'll effectively behave as a 96mm on a full-frame, but if you ever upgrade your camera body to an APS-H or FF, you won't be able to use it.