Kakashi - matching up against the current 5 Kage
Kakashi seems to have gotten very underrated. There was a time, long ago, when he was not that powerful. Since then he's gotten to be a Kage level shinobi.
Kamui particularly is his ace in the hole. He can warp someone, or better yet half a someone, so he sends half of someone into another dimension, and leaves the rest here. One shot kill. Kakashi's control of Kamui has gotten to pretty crazy levels. Even without Naruto, we've seen he can use it so precisely, he can teleport a single nail, moving at extreme speed, inches from his face before it hits him. He can catch two super fast Susanoo arrows aimed at him, out of midair. He can port a rocket, with a non-linear flight path, which is a large distance from him, all seemingly without line of sight of the rocket. Amazing stuff. The size of the area is now quite large too. Even without Kurama's chakra, the guy was able to teleport an area the size of the Gedo's head (or that explosion of Deidara's).
Nor is he held back by the "3 time limit" anymore. Even without the 9 Tails chakra, he was able to use it 5 times in quick succession against Obito, along with other draining techs like his lightning cutter and kage bushin.
This is without factoring all the other things that made Kakashi a great shinobi.
I think I'd take him pretty clearly over at least 3 of the current Kage. Tsunade he can just teleport her head to another dimension, then sell her body on the blackmarket. Mei will be dead the moment he looks at her. And while A has speed, let's remember that:
a) Kamui is frickin fast, and
b) using the sharingan to predict movements, Sasuke was able to dodge A's attack. Kakashi doesn't even need to do that. All he needs to do is use the sharingan to predict A's movement enough, that he can counter with Kamui (ending the fight). A also requires a moment to power up, and that moment is all the opening Kakashi needs to end the fight.
Maybe Gaara could get screens up, swap out with a clone, and counter before Kakashi could do anything, but Kakashi is pretty fast, so maybe not. Meanwhile Onoki might actually get one shot before he can react (and even with distance, Kamui has great range, so unlike most fights, distance won't protect Onoki. Overall, I think Onoki and Gaara probably have the claim to being the stronger characters, but one on one Kakashi can probably kill them both.
People need to really start re-evaluating Kakashi as a character, as he's gotten to the point where he's stronger than quite a few Kage.