worst ones I've owned:
Sigma 50mm 1.4 (Sold)
Sigma 50-500mm f4-6.3 (Sold)
Sigma 70-300 f4-5.6 (Made into a cup, also the worse of the worst)
I still got one Sigma left the 105mm macro... actually good colors and sharpness + good to manual focus with.
All of them shares the same fate of having horrible Autofocus, I wont ever buy another Sigma again!