Which should I get Super Mario 3D Land, NSMB 2, or OoT 3D?

[Funtime]

OoT for sure if you never played it. Mario 3D Land is better than NSMB 2 imo if you decide to go the Mario route.

Fire Emblem is amazing as well. Probably the best game on 3DS currently, but there's no shame in buying any of the 3 you mentioned instead. They're all good games.