Eiko is much better than Dagger. Eiko doesn't rely on Eidolons because she has Holy, and that does as much damage as any Eidolon Dagger has. Dagger is nice in the beginning of the game, but once you have a chance to train Eiko she becomes much more useful.

You don't really need a white mage if you have Auto-Regen and Auto-Haste, though. That depends on your level. If it's around 70-80 then you shouldn't even need a main white mage, but instead just a secondary one like Quina.