I used to have a spreadsheet that covered everything. I'll have to see if I can find it.
But your best best is a Duo R with an arcade card and Everdrive. It will allow you to play the largest % of the library with the minimal amount of stuff to buy. Out of the box, the Duo R will play all Japanese Hu Cards, and all region CD-ROM2 and Super CD-ROM2 games. The arcade card will obviously add Arcade CD-ROM2 games to the option list. And the Everdrive will add US Hu Card games as well (only the ROMs, not the actual cards - that would require a region mod).
With the 3 things I listed above, the only games you would be missing would be Super Grafx Hu card games (a total of 5 games), and LD-ROM2 games (a total of 11 which can only be played on ONE super expensive piece of equipment). No major loss there.
Another fairly new option would be to get a Japanese PC Engire, or either of the Core Grafx models along with a Super SD System 3. This would give you all of the above listed types of games. However, that metod only uses ROMs and disc images to play the games. The only physical games that setup will play are Japanese Hu Cards.
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Maybe, just once, someone will call me "sir" without adding, "you're making a scene."