If I could include the games I haven't played, I'm quite sure Spirit Camera would be my choice. From what I have seen it feels more of a snack between the main line games, and even if the story is a bit interesting, it doesn't hold up to the detailed mysteries from other games. The hardware of course limits possibilities, but there are so many great 3DS games that show you don't have to lack quality despite limits, so the game falls short in comparison.
From games I HAVE played, I would have to choose the original FF2. The fixed camera angles often got me make unnecessary turns and moving was bit clumsy, and with DCB adding more to the story I don't feel need to play the original anymore outside nostalgia kicks. Also the camera system and the spirit orbs weren't exactly my thing, upgrades especially are more smooth in later games. It's still a great game, but DBC has kinda taken its place on my shelf and instead of repeating same setting I'd rather spent more time with the more recent ones~