I am afraid you ask too much: 2.8, Auto focus, Zoom.
Yep, it's like the old saying - good, fast, cheap - pick two. Welcome to the Canon owner's ultra-wide lens choice hell.
After too many years and posts on this, I've come to the following conclusions:
- If you need the most versatile lens (f/2.8, AF, zoom, with low distortion) the 16-35 II is the best compromise. Yes, compromise. It's a nice lens if you use its strengths, but it will disappoint if you expect too much of it.
- If you shoot landscapes and don't need f/2.8, the 17-40 is the way to go, but again, is a similar compromise
- If you need the best IQ from a zoom
, order the Nikon 14-24 and a high quality (Novoflex) adapter
If you find yourself gravitating towards a single focal length:
- If you need the best IQ with AF, get the 14L II
- If you need the best IQ buy the Zeiss 15 f/2.8 or the TS-E 17, depending on your needs (filter compatibility vs. T/S)
I've left out the other lenses like the Zeiss 21 that are in this range to focus on the widest lenses, but same advice goes for them if that's your favored FL.
Personally, I settled on the 16-35II. It's not my best or favorite lens, but it's probably the most flexible lens I own. The low distortion is great and with the help of DxO / Adobe lens profiles, it's works very well for me. If I shot at 14/15/17mm all the time, I'd buy the 14L, Zeiss 15, or TS-E 17 in a heartbeat, because it would make a difference on large prints.