[daft_biker]

Do they say what focus distance was used for the charts? Macro lenses are often much sharper at infinity than minimum focus.....a MTF chart for the lens set at infinity doesn't tell you how it performs at minimum focus. Also, f/8 doesn't tell you how the lens performs stopped down further as macro lenses are often used at small apertures. I reckon that even if you understand the MTF charts those ones are about as much use as a chocolate teapot

From what I've seen shorter macro lenses are often sharper - the longer the focal length the harder it seems to be to make a lens focus down to 1:1. Longer lenses are often easier to use in the field though, particularly on larger insects that can fly away if you get too close. What's the best macro lens depends upon what you want to do with it.

I find something around 100mm is a nice compromise for general use.....gives good results and reasonable working distance.