The Tamron 90mm has a good rep, the Tokina 100mm also has a good rep, as do the Sigma 105mm and Canon 100mm. Any will suit your need, they're all very close to each other optically. My pick would be the Sigma (based on price). I wouldn't go anything shorter than 90/100mm to be honest - too short a working distance, too easy to spook your subject. Macro is my area of speciality and I've shot a LOT of macro over the past 4 or 5 years or so.
Dave
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