Which is the BEST ultra wide angle for Canon mount?

[behyx]

I'm looking for widest at 10mm or 12mm.

Thanks!

 

[Octarine]

EF lens or EF-S lens? Fish-eye or rectilinear lens?

 

[thoongeng]

You mentioned 10 or 12mm so I'm assuming APS-C format rectilinear ultra wide angle lens
Actually most of the ultra-wide angle lenses for Canon APS-C format are pretty good
So just depends on your budget

Cheapest can consider the Canon EF-S 10-18mm f4.5-5.6 IS STM
Or Canon's 10-22mm, price on 2nd hand market pretty low, just a bit more than 10-18mm, aperture a bit wider and less vignetting but no image stabiliser
Or Tokina 11-16 or 11-20mm f2.8 if you need the large aperture
Best, budget not a concern? Canon EF 11-24mm f4L - can also use on full frame, but big, heavy, not easy to use filters

 

[Octarine]

Samyang has a few prime lenses in the range of 10 to 14mm and Fish-eye models for everything wider.
http://www.samyanglensglobal.com/product/index.do#JTdCJTIyQ0FUJTIyJTNBJTIyMCUyMiU3RA==

 

[raydio]

You haven't mentioned whether you're looking for full or crop lenses. Regardless a look at Sigma lenses is also recommended.

I've owned both Canon and Sigma wide angle lenses and I've been satisfied with either. Sigma tends to be at lessor cost.