I think Zoroark is better than Ninetales, mostly because it can be found and evolved earlier and has higher special attack.
However, if you want a fast special attacker, Oricorio and Charizard are significantly better than both. They learn their special moves earlier than Zorua, they both learn work up, and the Flyinium Z is obtainable earlier than most other Z crystals. Charmander evolves earlier than both Zorua and Vulpix, and Oricorio is already fully evolved when you get it.
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