Having owned and/or shot multiple variants of both, I have to say that I prefer the AK. While the SKS is a fine rifle, it quickly loses its appeal to me when I start looking at modifying it from its stock configuration particularly when it comes to detatchable magazines. Aftermarket SKS mags can often have reliability issues and even when you get one that works well, I've found them to be slow and awkward to change. That still wouldn't be so much of a problem for me since it doesn't take all that long to zip in two or three stripper clips, but >10 round magazines on an SKS also, IMHO, screw up the balance of the gun.
Now, to be fair, I've not tried an SKS with one of the aftermarket pistol-grip stocks as those may help somewhat (though I rather doubt it due to how far forward of the trigger the magazine is located), but I've never been able to get past the look or rather cheap feel of most aftermarket SKS stocks.
As for the AK, a lot depends on which variant you get. In my experience, the GP-75, Mak-90, and Saiga is typically of higher quality than the WASR which seems to be the lowest-priced variant these days. I cannot attest to any difference in mechanical accuracy between an AK and SKS because I've never treated either like a target rifle, but for quick snap-shooting I've not found one to be appreciably better than the other. I've also never found the AK's ergonomics, while certainly not the best in the world, to be particularly problematic. Even though I'm a pretty big guy (6'4"), I've never found the Warsaw-length stock to be an issue. Finally, while the safety might not seem as ergonomic as that of the SKS, I've never had any trouble manipulating it with the first finger of my shooting hand and I do find it easier to use when wearing heavy gloves.