I say that if you think about it, Arceus is way to overrated and even with what all of you say, Mew is underrated. My logic is, with Arceus, for it to get a good type (I am saying this based of it's Attack and Special Attack) you need a plate, with Mew, you get good 1. Moves (It can learn any HM or TM) 2. Okay stats (I really don't calculate these much.) I think they are both beasts at competitive.
Now on to the looks. I think that we all know Mew is a little pink floating Pokemon, that most describe as cute, while it is undeniable that Arceus is a beast when it comes to looks. I mean come on, if these were regulars not uber Pokemon, if it came to looks.
Next is moves. Like a said before, Mew can learn any HM or TM. Arceus cannot, though it does learn epic moves like Draco Meteor.
So now I guess it is down to just what you think.