Buy Global no matter what, because when it goes out of print you’ll wish you had. If you can, start out with the old Milton Bradley edition (it is out of print but it was produced in heavy numbers) so getting even just the classic board and a PDF copy of rules is sufficient if you already have the Global game. Learn on Classic or the smaller versions first but have Global on hand because you’ll want to go further with the Axis & Allies series.
As far TripleA goes, it’s nice to have but can never replicate the feel or real life in game experience you will have playing the actual game. Also regarding TripleA; you still need to know the rules, while it uses the A&A game system, it is not officially an A&A game. The official game rules are easy to download to PDF and study, and playing the game via TripleA will require a decent knowledge of those rules, most player will expect you to know those rules as TripleA at this point cannot simulate every nuance of the actual board game. It’s not that TripleA is a bad way to play but it does require knowledge of the actual A&A rules.
My personal suggestion is to buy the Global set and Spring 1942 Second Edition and you will be well served. From there you can expand if it strikes you as something you’ll want to play.
Lastly, A&A is more of a hobby than just a game. While it doesn’t require the same type of effort of games like Warhammer, Bolt Action or Flames of War, it is more than just a simple board game that will leave you either frustrated and tipping over the table, or becoming a very enjoyable pastime and hobby. Â