I don't know much about the Krebs, but I had the same decision to make about half a year or so ago. I decided to go with a Bulgarian AK, for one reason because the supplies are drying up and I wanted to get one before the price became too outrageous. The only reason why I regret the decision is because my girlfriend decided that, after buying a Bulgarian Makarov, she was going to take over the AK because both were made by Arsenal.
Now, if (when) I buy another longarm, I'm looking long and hard at the Bushmasters as opposed to another AK but am VERY tempted by an M1A. The Krebs you mentioned (is that the one in the same magazine as the OSSs?) look very nice, but at that price you could get a good AK as well. So the price shouldn't be a concern.
You will probably (well, maaaaybe
) get a more accurate rifle out of the AR. More sighting options including better iron sights, better availability of parts, etc. More PC too, more gunsmiths can work on them, but the AK can be a do-it-yourself design due to its simplicity.
In general, you know that the saying is that AKs are more reliable and mine has not skipped a beat. Others swear by their ARs, however...
As far as the calibers, take your pick as to whom to believe. Both should be effective and the AK round will penetrate more than the AR round. Some claim that AKs zip through and through while the 5.56 will turn bone into grenade? 762x39 is going to be cheaper, at least for a while. My current SHTF rifle is an AK and I don't feel underarmed by it in the least. I can go camping with it and not worry about grime or muck, but I do take care of it as much as possible.
Whichever rifle you get, I would stick to the respective caliber that it was designed for.
The bottom line is this - if you could ONLY shoot one of them right now, which would you shoot? If you had both, but could bring only one to the range which would it be? If SHTF and you could only grab one, which would you grab? That's how I decided... Good luck, let us know what you get.