What do you mean by “new player”, and what is their general strategy game skill level?
I would vote Russia would be the “easiest” for someone totally new to Axis & Allies, or that’s just kinda there to roll dice. A brand new player has their hands full with turn order, how combat works, what units are what. By dealing almost exclusively with a ground war, you can spend more attention on fewer units, which is really a good thing for people just learning a fairly complex game. It’s enough work figuring out which enemy planes can get where without having to know or worry about how subs and damaged capital ships act.
Saddling someone with ANZAC alone would pretty much suck. At least give them France and China, so they can have some ground fighting somewhere. I wouldn’t do that to a new player, though. If you’re having to play with seven, given the minors to one of the vets, who can maybe actually do something with them.
For somebody that’s looking to be highly engaged and have fun, and maybe has played a previous iteration, Germany is hands-down the most fun. Your turn probably takes forfarkingever, but you get to conquer an enemy capital! Immediately! Loads of money, guys out the wazoo; boats, tanks AND planes! There’s a simple basic goal–take Moscow. It’s a ton of work, and they’re probably not gonna win, but it’ll be cool. Plus Germany has such a target-rich environment, new players often take the game in unexpected directions. For that reason alone, I like having brand-new German players, if they’re up to it. The Krauts have initiative–the opportunity to control the shape of a game you’ve never even seen played before is novel. Free of herd-mentality bias, if you will.