Originally based on a card game, the Legend of the Five Rings RPG became so popular in its own right that it spawned five different editions and a Dungeons and Dragons (3rd Edition) supplement.
This means that fans can experience L5R using either its original (extremely popular) AEG rules, the newer Fantasy Flight Games rules (based on their Genesys system), or with the Dungeons and Dragons 3.0 rules (or even 3.5 ... with a little effort).
Which Should You Play?
In general, we recommend the game's 4th edition. It consistently ranks in the top ten on RPG Geek ... out of all RPGs ever made. While it is out of print, it's still easy to find its products online. Also, because it had three prior editions, there's a wealth of supplements from those editions which can be adapted to fourth edition fairly easily. And if that wasn't enough, there's also a ton of fan-made content online.
In short, this edition offers more content, and a more popular rules system (one that was literally made for the setting) than any other option. But you can also read more about all three options below.