Nitrox is a specialty course $$. PADI no longer "requires" a dive, just the book work. I would say take the dive. I "feel" better diving Nitrox, maybe its all in my head, but I do.
Best to do your AOW in warm water, everything is easier in warm water.
My dog could pass AOW in the Caribbean or Florida.
But he prefers Jersey Wreck diving. Go figure.