I think Tamron lenses in general, for what you get, are the best bang for the buck. At least in 3rd party manufacturers that make autofocusing lenses. And Tamron lenses usually have VC.
They have their autofocus and VC stuff dialed in over there - at least with all of their newer lenses and in particular their SP line. I think a few areas where they excelled Sigma in the last few years are in Out-of-the-box autofocus performance, weather-sealing on most all of their lenses, and VC in most of their line-up as well. And then in the introduction of their Dock device. Sigma has of late (last 4-6 lenses) finally gotten much, much better in their autofocusing consistency with Canon bodies. And they've finally gotten on board with weather-sealing too. Their Sport line has always had it but now they are finally starting to include it in their Art series too...
Great time to be a photographer...