I haven't read all the 8 pages, but I just finished cleaning from shooting my CZ-858 and my Armalite M4. Had some newbies fire both as well. A few notes:
CZ-858 is easy to transition to. Great iron sights, like the SKS/AK sites, but more refined somehow, with a clear and fast picture. Mine came sighted in perfectly. Low recoil in the 18.5" inch model. Great balance (except for the long barrel), I love the way it fits people with regular to small frames. A dream to strip and clean, no complicated little pieces, doesn't crap where it eats.
But here's the bad part. First, I had the CZ-858 'Gremlin.' The distributor was very good and fixed it, but it was aggravating going to the range and experiencing those problems until it was finally fixed. I'm still not sure about the rifle's reliability. People with the milspec VZ-58 models seem to have better success. I've handled those carbines, and they are nice.
Second problem is the lack of non-corrosive 7.62X39. With clean ammo, cleaning is a synch, doesn't even really need to be cleaned all that often I bet. But with corrosive ammo, especially that Czech and Hungarian stuff, you need to clean whether you've shot 1 or 100 rounds. It took me 4 hours of cleaning my 858 yesterday, before I was satisfied. GET A CHROME BORE!
As for the AR, great accessories are available. I put a EOTech on mine, with no prior experience, in about 20 minutes, had it zeroed well before the end of the range session. Try that with a CZ-858. Putting quality optics on an AR is like LEGO. Same for other accessories. VZ-58 is more limited, though you can still get some good accessories for it if you look.
AR is more accurate, no contest. The VZ-58s seem to shoot between about 2-4 MOA with factory ammo (better than most 7.62X39 semi-autos), ARs can shoot well under 2MOA, depending on modifications and ammo.
I have to admit I hate the 'fit' of the stock AR. That grip is like a Glock, and the tube stock was not made for civilian shooters. But its easier to fit an AR to your body with mods than it is to fix a VZ-58 ergonomics. Controls are easier to reach and faster on an AR, though I find the VZ-58 design more comfortable overall.
The best part about the AR-15 is that it can legally use those 10-round LAR-15 magazines. That, and mag changes are way faster with an AR than a VZ-58 (though the stripper clips on a VZ would be almost as good if it was allowed to use 10-round magazines.)
FWIW, we found that the perceived recoil of a stock M4 configuration AR-15 is worse than a stock CZ-858, but it's probably different with the midlength and full-length AR-15.
In short, if you are looking for a rifle that can put a lot of rounds downrange fast, with compatibility for all the best optics, maximum customizability, and a lot of possibilities for overall length, get the AR.
If you want a blaster that you can take anywhere, get the CZ-858 or the new chrome barrel non-restricted model. The restricted model still has advantages as the VZ-58 series will fire all that cheap surplus that is half the cost of most AR-15 ammo. And the rifle costs half of a new AR-15.
AR-15s are more versatile because of their modularity, but are restricted and expensive. The quality of construction is higher, but it depends on how much you need. The military VZ-58 is pretty well built, but now you're talking about a restricted model. I enjoy firing my CZ-858 more than my AR, because I don't have to think about the cost of each bullet, and I can buy ammo in 1120 round cases for next to nothing. This allows you to experiment with improving your technique at the range at less cost than with an AR.
VZ-58 is fun. I don't know about practical uses, though I think I saw a video on CGN a while back of someone shooting a predator with a CZ-858, putting it down and avoiding potential harm to humans. Funny thing is that both are a real pain to clean, the AR because you've got to clean every nook and cranny if you want to feel safe that the rifle is going to be reliable, and the CZ-858 because of the corrosive ammo. You'll still clean the AR faster, unless the CZ-858 is using non-corrosive, in which case it wins.
I saw some discussion about terminal effects. That's really not my department. But keep in mind all us civvies can get is ball and FMJ ammo in both calibers anyways, for the most part, except for hunting ammo.