Final lineup

Germany is the best country to buy generals that way.

Bock is a decent general with great skills.
Heinrich can be comparable to Timoshenko if you set him up correctly.
Leeb is the second best artillery general in the game and is easy to get.
Model is a strong general, who despite being arguably worse than Bock, still packs quite a punch and has decent health.
Kesselring is strong on Carriers, and he is good to fix major cities, despite being seen as among the worst generals in the game.
Manstein is the most damaging general in the game, and he is very helpful in the early game if you buy him.
Guderian is the indisputable best tank general in the game, and spells doom for your opponents if you put him on any triple-stacked tank.
Rundstedt is the third best infantry general in the game and easy to get.
Rommel is the third best tank general in the game if you count Manstein. A god on deserts, and useful anywhere else.
Dönitz is the best navy general in the game and practically invincible in a submarine if you upgrade him.

I'm not sure if I can put Germany over the Soviet Union. I've tried both an all German roster and an all Soviet roster and I have to say that the lack of Konev (the second best general in the game) makes some of the modern war Senarios much much harder.
As for Tank generals I see Vatutin as a contender with Rommel due to the amount of tank skills available from the onset - tide of Iron is also an underestimated skill that has helped me pack more damage by hiding my weakened glass cannon Vatutin behind infantry and weak fodder. Rokossovosky is superior to Rommel no doubt, about equal to Manstein and slightly inferior to Guderian - He is positively very useful in modern and cold war senarios with air attack being very a potent especially when crossing the sea.
In a normal roster I would place him as second tank general after Guderian. The usefulness of Timoshenko doesn't need to be mentioned - he's allowed me to speed through missions and apply damage with my other generals to devastating effect.
As for my fourth tank general spot I've found Chuikov to have a strategic use in conquest and the larger campaign missions - hold a city and only attack enemies that will not counter attack (I buffed his health substantially and added crossfire and his pure survivability is insanely good to buy time for a thrust from my other generals in a different location)
As for Navy I buffed Vasilevssky's navy stars and applied rumour to make him a valuable hybrid without taking any of his infantry capacity away and use Kutnetszov to devastating effect with his own rumour and navy potential.
As for artillery Konev is a god and Zhukov is a very good artillery and hybrid, Govorov added to the mix as a powerful third Artillery and the German capacity for artillery outside leeb is laughable. When testing the two the Germany affinity for tanks is 1st and the Soviet is 2nd although it is close, and the Soviet affinity for artillery is 1st and the German isn't close.
Since artillery is second to tank however I have to place Germany and the Soviet Union as a draw for generals. Funnily Germany superceded every allied General at the start of ww2 although later I'm afraid the Soviets superceded the German strategic intellect post 1942. This comparison almost mirrors that development - an even match somewhat.

I think Zhukov (if you buy IAP) Rokossvesky, Vatutin, Timoshenko, Vasilevesky and Kuznetsov along with Govorov and Konev is a good lineup. But you need to upgrade some of them, as there are almost no defensive air generals, navy generals and so on.

I don't recommend Chuikov (a fireman general is never recommended, unless he is a tank air hybrid with good defensive skills).

I’d say monty is a bit overpriced. More people should buy vatutin imo. Vatutin actually starts out way stronger than monty at the beginning, and he’ll end up being manstein minus blitzkrieg at max strength