IMI will be more expensive, but I would much rather take my chances with it, since it's been around long enough to be a known quantity. IMI is excellent ammo, it just kills me that Botach has been the only place to get it. I heard rumors a few months ago that another company was going to start selling it, but I have no idea if this is true.
I have read reports of a few people who have used Igman and so far I haven't seen any major problems. But I would still be a little cautious about purchasing ammo that hasn't been on the market very long or heavily used. And be sure to avoid Olympic like the plague. There have been numerous reports of terrible performance and quality with this stuff. As far as Hot Shot, I haven't used any or heard much said about it. So for now I'd just go with IMI. You will likely be happy if you do and have excellent ammo.
-Charging Handle