While I don't know anything about Dragon Empires, Kara-Tur and Rokugan each have some advantages and disadvantages.
Kara-Tur was originally supposed to be in Greyhawk (on the other side of the world), but was later merged into Realms because that was the most supported setting. This helps Kara-Tur, because you can have characters from Faerun explore it, giving you an outsiders (gaijin) perspective, allowing it to open up for the players as they travel. It has a lot more asian cultures represented, giving quite a variety. The biggest downside is that there really isn't much story here, except what the DM devises.
Rokugan was an IP long before it was a D&D product. It has a rich history and detailed culture that is focused on primarily medieval japan (i.e. samurai). Depending on the timeline used, there are many interesting and detailed characters to use for NPCs, as well as a fully detailed story that spans several decades. There are a ton of resources available due to the AEG rpg having 4 editions, with most books expanding cultural, political, and historical lore. The biggest downside to Rokugan is that it's no longer a WotC IP, so there will never be any support for it, which is bad because the shugenja is a combination of cleric/wizard (with a dash of druid), and would need a full new class to be used properly (not to mention the courtier classes, but that's less important IMO). To run Rokugan would require a lot of Homebrew, and I don't believe most people would find it to be worth the effort (even if I would).
Kara-Tur was originally supposed to be in Greyhawk (on the other side of the world), but was later merged into Realms because that was the most supported setting. This helps Kara-Tur, because you can have characters from Faerun explore it, giving you an outsiders (gaijin) perspective, allowing it to open up for the players as they travel. It has a lot more asian cultures represented, giving quite a variety. The biggest downside is that there really isn't much story here, except what the DM devises.
Rokugan was an IP long before it was a D&D product. It has a rich history and detailed culture that is focused on primarily medieval japan (i.e. samurai). Depending on the timeline used, there are many interesting and detailed characters to use for NPCs, as well as a fully detailed story that spans several decades. There are a ton of resources available due to the AEG rpg having 4 editions, with most books expanding cultural, political, and historical lore. The biggest downside to Rokugan is that it's no longer a WotC IP, so there will never be any support for it, which is bad because the shugenja is a combination of cleric/wizard (with a dash of druid), and would need a full new class to be used properly (not to mention the courtier classes, but that's less important IMO). To run Rokugan would require a lot of Homebrew, and I don't believe most people would find it to be worth the effort (even if I would).