@tin-can-of-the-sea
Speed is the reason to buy Mechs over infantry. Units that can make the battlefield when dice are rolling are more important than those that are in the pipeline.
In order of usage:
1 - Germany. Not even close for anyone else. The need to get to Moscow with as much as possible as fast as possible plus the need to get to the Middle East afterwards makes Germany the mechanized infantry king. Useful for protecting West Germany, Normandy and Southern Europe too.
2 - UK Europe. Building units in South Africa and the Middle East makes UK Europe the mechanized infantry Queen. Having a bunch of mechs in the Middle East protects India, threatens the Caucasus/Volgograd and protects Egypt.
3, 4, 5 and 6 - Russia, UK Pacific, Japan and Italy. Russia, maybe 3-4, because a few fast movers with tanks helps project force against small German detachments. UK Pacific, maybe 5-6, to help fight for Yunnan and Kwantung while still protecting India. Japan, maybe 3-4 to help get control of China faster. Italy, maybe 4-5, to send to the Russian front as can openers and West Germany to be able to move from West Germany to Normandy to Rome as needed.
8 and 9. France and China. If France ever gets to build infantry is the way to go. China can’t build mechs so they are last.