First, I want to thank you all (yes, all) for your answers (even the … inscrutable ones).
Some of you have discerned (or think you discern) an ulterior motive to my posting these questions. (Well done, even if you so were far off the mark to provoke an off-screen cat noise.)
As I said before, I aggregate more than collect. It might be nice to afford some of the genuine MVS stuff at some point (the AES/NeoCDs aren't on my radar). As I might have mentioned, the Neo Geo is not something I paid attention to when it was current; I have no nostalgia for it, no history, and no significant experience. But I do see it as a blank spot in my personal knowledge (like the entirety of Sega), and am curious about cartridge-based hardware.
But back to that ulterior motive.
See, I do have one. I'm looking for ways to dissuade my nephew from playing Roblox and am building a device without access to the internet which will—ideally—divert him somewhat. Now, I do feel that younger folk can have a legit interest in games, but Roblox specifically fills me with concerns, none of which was allayed when I questioned their staff at the expo floor at GDC 18.
You might disagree, and believe that Roblox is harmless, but it consumes too much of his time, and that now includes school time. I don't intend to punish him for gaming, I intend to guide his interest better than a seedy commercial enterprise should. An uncle (even a nuncle) should at least show him how wide the horizons for games can be.
Hence my interest in your interest. I should have asked about platformers, too, but my impression is that the NG doesn't have a lot.
Now, am I going to set him up with a real MVS with a few carts?
Absolutely not. He keeps pizza crusts in his room, that would be absurd. But an emulator is a wonderful thing.
—Scott
But here are my personal favorites in each category. 
