Even on a 1.6x format camera, I consider the 50-60mm lenses a bit short. The lens to subject distance is very small; scaring little creatures and making lighting difficult. Additionally, the Canon 50mm f/2.5 lens will not focus for 1:1 imagery without an adapter.
Although the 150-180mm range gives you great lens to subject distance; these lenses are pretty heavy to hand-hold and are also relatively expensive.
I like a 90-100mm lens because it is light enough to easily hand hold, gives decent lens to subject distance and is not astronomically expensive.
I personally use the 90mm f/2.8 Tamron SP Macro lens and love it but, I know that I would also like the 100mm Canon macro. Both these lenses can double as short telephotos and portrait lenses.