This is all going under the assumption 4 people have played other A&A games before, but not Global:
Axis:
Whoever plays Japan will do one of two and possibly both things to lose for the Axis in the Pacific: Run their navy into the ground too early, or wait too long to expand under the idea of keeping the US out of the War as long as possible. Both of these are pretty unforgiving for Japan and can turn the entire Pacific board into an afterthought for everyone. To me, this makes Japan one of the hardest to play with zero knowledge about how Global works.
Germany is probably the most forgiving if anyone has even the slightest idea that Germany is supposed to capture Paris, try to sink as much of the Royal Navy as possible, and buy as much armor as possible to take Moscow. These are pretty typical strategies in most A&A games, so it shouldn’t be a far reach to play Germany rather well for the first time.
Italy is a toss up because it’s early battles are very 60/40 or 40/60 odd types that Italy could be run into the ground early, or could become a monster by round 3-4. Much of Italy’s success for a new player (and really even experienced ones) is very much dependent on how intent the UK is on harassing it versus what the Germans are willing to do to prop up their starting assets.
My ranking of Axis, Hardest to Easiest:
1. Japan
2. Italy
3. Germany
Allies:
Americans never lose, but they never really win either. They just push everyone around on whichever side of the map they get involved in, but without 100% into either map, they really are just an irritation to be dealt with. You cannot really mess up as the Americans, making them very forgiving but potentially very bored if someone makes you wait until the 4th turn to attack. That’s entirely possible with people new to the game seeing the chance to keep the Americans out of the war that long.
UK - London
Pretty easy game for UK - London players. I highly doubt a new German player will Sea Lion, so I’d expect UK players to do fairly well. Still, a determined march on Moscow by the Germans requires UK intervention which a new UK player may not realize until it’s too late as they’re trying to build a fleet and units to land on Normandy. UK also may overlook Italy and Africa early and find itself working out of the IC in Africa to save the continent.
UK - India
Considering it is highly unlikely to see a new player behind Japan go for the KIF by Round 3 / 4 effectively, UK India should have it pretty easy - especially once in the War. India’s long play is really contingent on taking DEI, so depending on if a new player recognizes this or not will probably make the difference between staying afloat in the Pacific or turning China into a monster that kicks Japan off the coastal territories.
China is, well pretty boring. Provided a new player understands holding the Burma road is the key to their success and Japan does not do well in contesting it by landing new units near Burma each round, China could handle Japan on it’s own. China could fall just as fast against a well informed and strategic Japan without help from the UK. I’d bet the likely scenario for a game of all new players is China is building Art in Round 3.
Russia’s difficulty really depends on the effectiveness of a German player. A Germany that takes France and then goes all in on purchases to take Moscow and DOW on G3 is going to be hard for Russia to play against. Russia had two rounds of purchases that could be really, really bad for Russia if they bought the wrong things or thought it was a good idea to contest the starting borders. If Germany tries to DOW on G2, and Russia decides counter attacking is a good idea, Russia could be a fun strategic Cat-n-Mouse play ripe with risks that could make or break the battle in Europe on any round. Overall, Russia could be very difficult to play, or very fun, and sometimes really boring if / when you reach a stalemate sitting on Moscow.
ANZAC is another pretty boring nation to play overall. Severely limited by economy and proxy to ongoing events, a new ANZAC player may get involved in matters with Japan it has no business doing early in the game. Losing its Navy early could cripple the mid-late game for ANZAC due to inability to expand to DEI. Assuming the player is new, I’d bet this happens. Bright side, is losing the fleet and fighters for ANZAC isn’t the end of the world because ANZAC is unlikely to be a focus for Japan for many rounds. It just makes for a boring waiting game which assuming Japan makes some mistakes along the way, will just turn the game into a stalemate in the Pacific.
My rankings of Allies, Hardest to Easiest:
1. Russia
2. UK - London
3. UK - India
4. ANZAC
5. China
6. USA
Overall rankings, Hardest to Easiest:
1. Japan - It fights alone in a single theater against multiple nations.
2. Russia - One misplay early could load the deck for Moscow to fall.
3. UK - Russia needs the UK’s help more often than not. Most think landing on Normandy helps, but often it does not. UK could lose Europe, Asia and Africa with a few misplays.
4. Italy - A few strategic gaffes could spell the end of Italy’s expansion, and failing to recognize that defending Germany’s backside is just as important if not more-so than it’s own expansion could lose the game for the Axis in Europe.
5. China / ANZAC - Both are pretty minor players. One has a huge early game impact, the other can have a huge impact on a mid-late stalemate in the Pacific.
6. Germany - Fairly forgiving in the overall sense of the game. You can make multiple errors and still sack Moscow.
7. USA - Just as forgiving as Germany, but that is because you can just buy more stuff. Proxy to both conflicts requires planning purchases turns in advance which is about the only difficult thing about the US. You won’t win on your own, but you’ll almost never lose the game because of your decisions.