Until early 2015, it was really tough to recommend a decently priced wildlife lens. Now, you have options galore. The Canon is the top of the pack for build quality, but the Sigma has a more versatile focal length. The Tamron 150-600 should not be ignored as it is MUCH cheaper and 95% as good optically. I say save your money and spend $1,000 on a wildlife trip to Yellowstone.
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