Sigma image quality is bad, due to its bad quality control, but in rare 1 out of 20 unit, there is a perfect sharp unit. So far I only meet one unit sharper then original brand lenses. But the rest of sigma I have tested is terrible soft! Especially at 200 end.

Tamron sharpness is a lot better, for stage/event shooting, as long its bright enough, Tamron won't go hunting, and event usually is noisy and loud, who can hear ur AF sound?.

Get Canon with IS. Let it be mark I or mark II. Non IS lens will drive u crazy thinking yu should have gotten IS in the first place.