In both Colosseum and Gale of Darkness I've seen two different arguments. One side argues that Shadow Pokemon should ideally be the only Pokemon that you use because they're always on a good part of the level curve and they're SE against whatever you don't want to catch and they don't do much damage to whatever you do want to catch, while others argue that you shouldn't use them because unlike your starters they won't have the advantage of being overleveled. Is there a balance here? Does the correct choice vary between games?