Have owned 3x 100-400's and I think after a number of years of commenting on it I think people know I think it's too inconsistent across copies and potentially a bit too softy wide open to recommend ... for the price! But there are plenty of good sample images so go for it if you want another one. Had the 150-500mm OS on Nikon and Canon and both great OS and good image quality ... and 100mm makes a big difference for safari shooting, which is what I need a long lens for. My choice would be the Sigma first for sure. But there is a new 50-500 OS out and worth considering that too if reviews/samples stand up. I had the old 50-500 and really liked it. Adding OS should really boost it, but then you're likely in red ring territory.