I've never seen either lose zero but depending on zoom range the Athlons are dark at higher zooms. A friend has one of the $1200 60x Athlons and it's good on the high end but the 10-40's have all been useless above 32x.
The Arkens in our group are 6-24's and have been rock solid.
Edge to edge clarity and build Quality are better to me On the Arken until you get to the Cronus not to mention much better feeling turrets. I have ran both for quite some time and still do.