Upload & Sell: Off
I've used the Canon 17-40, 17-35, 16-35, Tamron 17-35, and the Samyang 14 from your list. The only one I still own is the Samyang, and it's the one with the absolute best IQ in your list. If I had to get one lens off of your list, it would be the Samyang 14. If I had to pick from the zooms from that list it would be Canon's 16-35mm. In my experience, the IQ is just "good" not "great" on all of the zooms you mentioned. The reason it would be the 16-35 is because of the 2.8 (for what astro work you want to do), the build, and the superior AF.