Yeah, I agree that a newbie should play on the Allies. The Allies require teamwork and they have to help each other out anyway. With a newbie on the team as a weaker country you can come to the rescue or try to fix his mistakes.
Every country has a role to play and can screw up the game for their side. I’d give a newbie the UK - It’s more fun than buying all INF with USSR and they can follow the US lead in the Atlantic. The US can guard Africa and UK can send planes and men to Karelia or Western Europe. UK isn’t threatened, either. Watching the colonies go up in flames kind of sucks, but your Allies should protect those.