Best ultra-wide-angle zoom

I have the Tokina 19-35. It's okay...nothing to write home about. It does a surprisingly good job holding edge focus, but is definitely much sharper in the middle, especially around f8. At 19mm the distortion is plainly obvious at the edges...and I'm talking borderline fisheye. If I were going to buy something wider, there's no question that I would go aspherical.
Canon 16-35 f2.8L MkII

for wider look at the 14mm L

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