For normal macro, Canon’s 100mm macro lenses are very good, and the 100mm L is especially praised for sharpness and autofocus. But for an insect’s eye, a standard 100mm macro usually won’t go far enough on its own because it tops out at 1:1 magnification.

For true extreme macro, the Canon MP-E 65mm is the lens repeatedly recommended. It goes beyond 1:1 up to very high magnification, which is what you need for subjects like insect eyes.

The tradeoff is that extreme macro is difficult: depth of field becomes extremely shallow, focusing is challenging, and lighting is a major issue because you’ll often stop down to around f/11 or smaller and the lens can be very close to the subject. In practice, low-light available-light macro is not realistic at these magnifications; you’ll usually want an external light source such as a flash.

So: if you want the highest magnification, look at the MP-E 65mm. If you want a more versatile general macro lens, the Canon 100mm macro—especially the L version—is still an excellent choice.