The covenants need to make sense - they have to give you something substantial in order to motivate you to actually stick with them. For example, an infinite Cracked Red Eye Orb would do it.
When it comes to existing covenants, then Darks Souls 1 has the best of the best (e.g. Darkwraith). While Bloodborne could do completely without them, as there was no real point to covenants in the game at all.