I am trying to decide whether to get the L version or the non-L. Does anyone here have experience with both? Is there a difference in sharpness/overall IQ? It's for Canon 6D, so I'd especially like to hear about comparisons using 5D MkII or the 6D.
I've had both. There's really no difference in terms of sharpness/IQ unless you're looking at the extreme edges. The IS is nice and has a better balance. The non-IS lens felt a little clunky, but that has nothing to do with the IQ.