It's both personal preference and a difference in lenses.
Generally speaking, the longer the focal length of a macro lens, the better. People say this because the longer focal length means you don't have to get so close to the subject, a real advantage for insects and other small wildlife etc as you are much less likely to disturb them.
The Canon 100mm macro is very expensive though. Have you considered something like the
Tamron 90mm f/2.8 or the
Sigma 105mm f/2.8 both of which are under £400 and both are sharper than the Canon 60mm.