Day 14: Which RPG do you prefer for open-ended campaign play

Dungeons and Dragons. Any version.

• Want to take a sailing ship to the edge of the world?
• Want to stop a zombie apocalypse?
• Want to start one?
• Want to ride dragons into battle against evil?

From low-level rat fighting to building a castle and running a barony to invading the Nine Hells there's a ton of options for a campaign and nearly infinite directions the players and DM could take a campaign. I know because I've done it as a player and as a DM across a bunch of versions of the game.

Runner up
Any superhero game. The universe is yours! In fact, multiple universe may be yours! You can do basic street-level crime-fighting heroes if you like, and you could scale it up to repelling an alien invasion and invading the Nine Hells here as well!