I say Kimahri, because his sphere grid sucks. By the time he's done with his sphere grid, everyone else is about halfway through theirs. So why would I want another white mage when Yuna's already better? Why would I want another fast attacker when Tidus does the job just fine? It does nothing but prove that the sphere grid is the worst level up system ever (since after a while, your characters lose their individuality. read the above post about Yuna doing 99,999 damage), but at a faster rate.