Arceus vs. Mew?
Hmm...
Well, Arceus has higher stats in EVERY STAT, a movepool the size of a lake, unique move that always takes STAB, and... is based on a mystical giraffe.
Mew has lower stats, a movepool the size of an ocean, no unique moves at all, and... I don't know what this thing's based on.
But I prefer Mew because it has a LOT more move options. Legit-wise, it gets every TM, HM, and Move Tutor Moves, which gives it some more options than Arceus (Mew gets TM 45: Attract, whatever that'll do...). Glitch-wise, Mew gets TRANSFORM, which allows it to get up to 3 Sketch-able moves through my favorite 4th Generation glitch. Meaning, Mew can get: Dark Void, Judgment, Seed Flare, Psycho Boost, Spore, Sacred Fire, Aeroblast, Spacial Rend, Dragon Dance, Cosmic Power, Shadow Force, Roar of Time, etc.
So screw Arceus, Mew is still better. Plus, I liked Mew since Generation I. I never liked Arceus to begin with. Oh, and I like the shiny Mew better than shiny Arceus.