I haven't got this lens now but had it for 2-3 years and also have the other Canon macros...100/2.8, 180/3.5L and the MP-E65.
The EF-S60 is just as sharp as the others and won't disappoint you. It would probably be the best choice if you also intended it to have a second use as a portrait lens.
It does have several disadvantages though...maybe they're not an issue for you?
It won't take a tripod ring and the working distance at 1:1 is quite short...9cm ! The final drawack is that it can't be used on a full frame camera.
I would go for the EF100/2.8...gives you 15cm working distance at 1:1, can have a tripod ring if required, useable on FF bodies, IQ is reasonable when used as a medium telephoto on a crop body and has internal focus (so does the EF-S60 but the Sigma's don't)
The EF100 will cost you about 50 quid more than the EF-S60 but is probably worth the extra.
Now the obvious question....what do you want to shoot?
Bob