The canon 50mm f1.8 (new) is slow to focus and if used sub < F5.6 or > F8 chromatic abberation and purple fringing spoil most shots, reason = plastic lens elements and cheapo AC motor.
The mk1 50mm F1.8 (metal mount) if you can get a nice one, is optically far superior but not really useable under F2.5
The 50mm F1.4 also cant be used under F2.2 without compromise, but barrel distortion is acceptable and chromatic abberation is tolerable and bokeh is stellar, has to be the best value/performance in the 50mm line up
I dont own a 50mm F1.0 L so cant comment on that.
For me the 80mm F1.8 is my most used prime