“It Depends” is the best answer I can give you.
If we’re talking strictly OOB, no bids, Anniversary is the more balanced game any way you split it.
However, far more work has gone into developing G40 into its current state than has gone into AA50. AA50 is balanced by the community simply by adding bids for the Allies (varying by scenario and whether you play with NOs turned on/off). G40 is balanced by the community by developing entirely new rulesets and altering entire mechanics to create what is essentially a completely different game to what you buy in a store. Despite these efforts, the Axis still are seen as having a massive advantage in G40, and most ways to play AA50 see the Axis in a similarly dominant position, with the Allies needing large bids to compete.
NOTE: Take what I said above about G40 with a grain of salt though, I don’t play G40 competitively. However, most members of the community would probably agree with me. Just because a game is more or less balanced than another does not speak to the amount of fun you can have playing said game. G40 is the most popular version of A&A for a reason.
In my opinion, if you want a balanced scenario, play the 41 Scenario of AA50 without National Objectives. This should give a fair challenge to both sides, as the Axis need to make the most of their massively superior starting forces to narrow the absolutely massive gap in production between the two sides (Axis: 58 (G: 31, J: 17, I: 10) Vs. Allies: 113 + “7” (R: 30, B: 43, A: 40, C : “7” (recall AA50’s odd rules for placing new Chinese Units))). The Axis might have twice the starting punch of the Allies, but without NOs its going to take quite a bit for them to make up the 50+ IPC difference (that’s ~25 IPC of territory they need to capture).