George Thomas was an able corps commander and army commander, but he never made his mark commanding a campaign on his own. He was under Rosecrans at Chickamauga, under Grant and Sherman at Chattanooga, and under Sherman at Atlanta. His actions during Hoods last campaign in Tennessee were good, but not good enough to break into the top 5 or so.
As for the rest, Sherman was good. I rank him number 4. Hooker, Buell, Rosecrans? Same level as Bragg, Johnston and Hood. Nowhere near the top 10. Meade was overshadowed by Grant so it's really hard to judge him on his own. He may have been an able army commander, but didn't match up with Lee. Grant did. Burnside? Even Burnside thought he had been promoted far above his abilities. Porter is a might-have-been, like Reynolds and a whole host of generals on both sides who were killed or had their careers derailed at some point. Who are we missing? We're missing a lot, on both sides. Sherman had a whole raft of excellent corps and division commanders who nobody hears of because they fought in the west. Logan, Blair, McPherson, Crittenden were but few.
All in all, I think that the Union Army was every bit as strong, or stronger, than the confederacy at the brigade, corps and division level. At the army level, I have to give it to the Union because looking at the confederat Generals then it's clear that it's Robert E. Lee and the seven dwarfs. No other confederate general came close to Lee, and damned few Union ones. That's why Lee is third, and I don't mind ranking confederates 2 out of the top 3. But it's Grant at number 2 that made Northern victory inevitable.
Yep - the numbers game. Lee knew it, Grant knew it. The Southland was losing her supply of young men and great leaders!