I bought several macro lenses to compare all of them a few months ago. Without a doubt, the 105mm focal length was the most versatile in my opinion, and can even be doubled up with an extension tube for greater than 1:1 magnification. The Tamron 90mm is very good for crop sensors, but just a tiny tiny bit too wide for full frame in my personal opinion. Then again, it is optically on par with the Canon and much less expensive.
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