Canon EF 24mm f/1.4L II or Sigma 24mm f/1.4 DG HSM Art Lens

I'm trying to decide between the Canon EF 24mm f/1.4L II or Sigma 24mm f/1.4 DG HSM Art for some wide angle, low light work I'm going to do. Normally I'd just use my Nikon D800 and the Nikon 24 f/1.4, but I have access to a Canon 5DS R. I've done some looking around online and it's no surprise that some prefer the Canon and some prefer the Sigma.

I'm asking for advice here because with my D800, I shot the Nikon 24 f/1.4 side by side with the Sigma 24 f/1.4. Aside from the fact that the Sigma needed a fine tuning adjustment of either + or - 10, I found the Nikon to be the sharper lens, especially wide open. I"m not sure if I had a bad copy of the Sigma, or if it just needed to be calibrated with the dock. On the flip side, I once tested the Sigma 35 1.4 side by side with the Nikon 35 1.4 and found the Sigma copy to be better.

Anyways, back to Canon vs. Sigma. Does the Sigma show improvements over the older design of the Canon? Back in 2008, I used the first version of the Canon 24 1.4 and found it to be a great lens. I guess I could always rent both lenses, but would prefer to stick with one.

Armchair reviewer, but I would go with what the Digital Picture says:

The 24 Art's price tag is just over 50% of the price of the Canon and just under 45% of the price of the Nikon. That factor alone will make the decision for many. This lens' biggest disadvantage is AF inconsistency.

Their relative performances seem to be pretty close. This is not the ART lens that people talk about with awe such as the 50mm ART or even the 35mm ART. In your shoes I would probably try and pick up a secondhand Canon ver II, as AF inconsistency is very irritating in the long run and it may make you regret not having paid the extra. If, of course, you will be largely manually focusing then this concern is moot.