I personally don't think Sylveon will be a good Pokemon to have on my team, just to fill the dex.
But Xerneas will probably be the strongest. But if your talking about design I don't know probably Xerneas as well. --- I am the bone of my sword. Steel is my body, and fire is my blood. I have created over a thousand blades. Unknown to death. Archer - Unlimited Blade Works
I get this feeling that as it stands, Mega Mawile is horrifically underrated. So I'll probably be tearing teams apart with that. --- R- Official Slowpoketail Vendor Official Mawile of the Pokemon Boards.