As much as I like Krox I have to say go with the Ancient Steg. 7th edition Krox were great! 3krox getting a flank charge into almost any unit would be 4-5 dead. But with Initiative vs. GW for striking order Krox just arn't hard enough anymore (unless you are flanking Scaven slaves/clanrats/spears). Ancients has those drawbacks as well but it has: higher Toughness, 2+AS, imact hits, great blowguns, and terror. All that on a 50mm frontage. Don't get me wrong, I still have 4 Krox in my list. They just have some ablative armor(ie, 48 Skinks) to soak up some hits.