Both of them have a sharp air to ground game, it's hard to say who's superior, there are times where one ***** the other, Fox can spam (RAR, is it..?) back air and give Wario troubles, all the same Fox does not wanna be up over Wario 90% or higher.
But Wario's aerials isn't his real strong point, it's his aerial movement which makes his aerials shine so much, he can poke very effectively, throw out some test shots and just come in when it succeeds, however, Fox's speed allows him to simply wait for an opening and charge in sex nuts and ****** strong.
Plus Fox has the advantage of camping to properly place his opponent where he needs them to do whatever.