Fox is the hardest character to play? Idk, I think playing ness at a high level's a lot harder =PPPPPPP (Considering it's nigh impossible to win against a good player xD)
But rather than misinterpreting what you just said:
It depends on the person really. As said in the post above yours, fox is about speed. If you have the finger speed, the timing isn't particularly difficult, because most of the time you won't be doing it too fast for fox (unless you're insanely inhuman). Falco on the other hand, is realllly easy to end up going too fast with, and you have to learn specific timing instead. If you have slower fingers, I suppose falco would be easier, but if you have faster ones, fox might be more natural to you. Just a random example is double shine pillaring... I tried it in training mode, and after just a tiny bit of practice I could do it with fox without any trouble at all. With falco, on the other hand, I would have to find the exact timing, and I frequently ended up doing it too fast/slow. Obviously after some practice I got it down with both, but falco was definitely the less natural of the two. Not to say falco's harder, but it depends on the person.
Edit: @Roneblaster, what are you talking about, I thought falcon was a sheik counter... =P =P =P