Mt Spokane Photography said:
The Sigma 50mm f/1.4 is optimized for APS-C , while the Canon 50mm f/1.4 performs better on FF.
Reasons to upgrade are
F/1.4
Better build and reliability.
Downside to Sigma - commonly have AF issues (for those that check) and need to go to Sigma for adjustment. None of them have AF that is outstanding.
+1....I turfed out my EF 50 f/1.4 and replaced it with the Sigma 50 f/1.4. What a wasted exercise. Not only was the Sigma heavier, it took up more room in my bag than the beautifully compact Canon 50. Should have kept the Canon...
I shoot on FF and found the Sigma AF erratic to the point where I just couldn't trust it on jobs. Which means I never used it. When it nailed focus it was terrific, but the inconsistency was the killer. It's gone now, replaced with a 40 f/2.8 which I also hardly use. But at least it's small, dependable...a lens I can trust.
Really, I'm a zooms shooter with primes kicking in at the long telephoto end. The new 24-70 f/2.8II is such an extraordinary piece of glass that primes in this range seem redundant. I'm even looking at disposing of my 24 f/1.4II because there is little need for it any more. A f/2.8 or even slower lens is not the liability it used to be when we were tied to 100iso if we wanted quality files. Now with our new best friend,ISO, carefully shot/exposed images done on sky high iso settings can deliver superb commercial quality files.
-PW