This. I also see Onoki like the strongest Kage. I mean, this guy is a monster. He is growing old, his back hurt, but he even with that, he fought Muu, and even without jinton during a long period, save an entire division against Madaras meteorite were he was totally crushed, and was still capable to fight Madara the time other kages came. And until now i think he is the one who do the greatest job. Protecting everyone with his golem, the only kage who was able to wake up and save everybody against mokuton by destroying the flower with Jinton, give a fatal blow on Madara with Jinton(even if Madara did it on purpose). I mean Onoki is too underestimated i think. He is by far the strongest kage right now. His jinton is too powerful.I say Oonoki. A's not touching Oonoki mainly because A cannot fly. Although Oonoki may throw out his back in which case I say Gaara wins.
I think Mei would be blitzed by Raikage, zapped by Jinton, or punched by Tsunade (loses to Oonoki, Tsunade, A)
Tsunade doesn't really have a defense to Jinton. She'd need to get close to Gaara. So (She loses against Gaara and Oonoki.)
Gaara could be beaten with Jinton. (Loses to Oonoki)
A would lose to Oonoki's Jinton, Tsunade in a fight, Gaara's Sand (which has stopped him mid-attack before). Though I suppose if Mei catches him with a Suiton that may pose problems for raiton cloak. (Loses to Oonoki, Gaara, Tsunade)
After that, i see Raikage stronger, then Gaara, then Tsunade, then Mizukage.