I recently acquired a Sony a6600, and I need a good all around lens; I do both video and photography. I will use it primarily as a travel lens, for planespotting, concerts on occasion; and every once in a blue moon in a more professional setting. Since I will be using this as a travel lens, I really like the size of these two lenses. The two main concerns I have are:

• Image quality: just how much sharper is the Sigma vs the Sony?
• OSS: how much of a benefit is there when the OSS is combined with ibis?

If the OSS combined with ibis gives significantly better results over ibis alone (since the ibis by itself is pretty terrible), and if the image quality is not too much of a downgrade, I would lean toward the Sony. That said, if there is significantly better image quality with the Sigma, and just a negligible benefit regarding OSS on the Sony, I would lean toward the Sigma.

I am not too bothered by the lack of reach on the Sigma, nor am I too bothered by the slower and non-fixed aperture of the Sony.

Edit: if there is another lens that is similar to either one of these that I am overlooking, please let me know. Also, I have been successful in adapting EF-mount lenses, so I am open to a similar EF-mount lens as well.