Germany and Russia are the two hardest.
USA is the easiest
Agreed. I would never attempt to play Russia or Germany without an oddscalc. Karelia needs to be managed with the greatest of care (as Russia, I keep at around 55% success rate against German attack). And slowing down the Japs with Russia is almost an artform if you’ve seen it done by some of the best players.
Germany is even worse. If you have WE, Berlin, and EE locked down, it’s probably by a razor thin margin and you need to balance everything like a juggler. Most of the time, I don’t have enough troops to hold all 3, so I trade WE every round with UK or US. Eventually, the Allies will build up Spain, or attack WE en masse, forcing you to clear them out. Either way, you’re going to cede EE or WE, and then the end is in sight. The goal is to prolong it as long as possible to get as many tech rolls with Japan as you can.