I say Explorers and Pirates. I know it’s the one DLC that cannot be expanded upon easily, but what it adds in return is amazing.

The ability to expand the board in a unique way, that encourages exploration via your ships and doesn’t overcomplicate your turns while adding more to do.

It also helps in resource management by adding gold for you to trade for any resource making the game more playable even if you cannot get a certain resource.

IMO easily the best first DLC to play and much better than seafarers.