The easiest way to go: AES and MVS. For me, anyway. I've had an AES and a Neo CD for years. Now with the Phantom-1 converter, I can basically buy any game I want at whatever price. You can't get all the debug options without a debug chip, but you can play the games nonetheless.
Furthermore, it balances things out. You want the nice cases, manuals, and all, you have the option. You just want to get your hands on the games, you have that option with a Phantom-1. The AES+Phantom-1 combination might not be the cheapest, but it gives you a freedom with your game purchases. Run with the older AES carts and the newer games on MVS (that's what I'm doing now).
Now, don't take this as me saying I'm anti-MVS hardware. I'm just a bit biased since I had an AES for years and I really didn't want to sell it (so the Phantom-1 was the ideal upgrade). I definitely would go with your idea of getting into both AES and MVS. It just gives you tons of options as far as what to buy.
Richard