If you want to shoot a Canon full-frame really wide, this is the best lens you can pick up. It’s much sharper than the 16-35 f/2.8. For a 14mm lens it has a very reasonable 2% barrel distortion (half of what the Nikon 14-24 f/2.8 zoom has, for example). It’s an excellent lens. Pricey, but then there’s really nothing else this wide and this sharp for Canon shooters.

If I was shooting architecture, though, I’d really consider the Canon 17mm f/4 TS-E which has virtually no distortion and the added benefits of tilt and shift.
March, 2013