I have all 4 covenants over my first four lv60 chars, only 2 of them are in the "best" covenant. Later chars mostly get optimal covenants, just because... why gimp them, I got all the story already.
Currently I am leveling my third paladin, all of them are exclusively tank, all of them Kyrian. Coincidently the "best" covenant is the most fun too. Even if Kyrian was numerically the worst, I would always choose Kyrian because nothing is more fun than Divine Toll. Whoever came up with that deserves a raise. I wish every spec/covenant combo had such an ability, no other class has a covenant button that fun to press.