I feel there is a lot of symbolism in the Orre games. Before I answer the question, let me explain how I see it.
Nascour and Evice both are symbolized by the shadow Pokemon they own.
Nascour- Like Metagross, Nascour is highly intelligent. He is the false ruler, but he has four combined minds to work with: Miror. B, Dakim, Venus, and Ein. (Gonzap was basically running a fool’s errand, and therefore isn’t part of this group.) As the pseudo-ruler of Cipher, he controls everything with an iron fist.
Evice- Evice is a power hungry mayor and the ruler of the Cipher syndicate in Pokemon Colosseum. Evice has the power to do what he wants, but he is hungers for more. He is similar to Tyranitar in that fashion.
Pokemon XD seemed to be a follow up for Pokemon Colosseum in more ways than just being a sequel. Evice was the next short old guy to be the bad guy, and the game characters themselves have anticipated it. However, the real spoiler is the standing of his two sons, Ardos and Eldes. Ardos was a devil while Eldes was the angel. Ardos wanted to do harm and annihilate the opponent, while Eldes wanted to do the right thing and turn themselves in.
I say Evice. A lot of the reason is because of Greevil’s possible guidance from Ardos. Evice knew what he wanted; Greevil was set on a path (perhaps).
Maybe I am over analyzing the whole thing, but I find it more fun that way.