If Tamron built this lens to outperform the Sigma offering then they succeeded with full frame cameras. The gain in performance over their rival’s offering is less noticeable on the APS-C cameras. Despite that, the image quality is a slight improvement over the Sigma. Given the longer range and similar price, it’s a pretty impressive achievement. 

The Tamron even outperforms the pricier Canon lens on the full frame Canon EOS 5D Mk III though it’s less convincing when compared with the Canon EOS 7D. There’s likely too little in it to switch but for first-time buyers the new Tamron is attractive proposition.