I can't really say Ridorana is the last dungeon because Bahamut is. The length should not really count here because Lightning Returns does also not have a very long final dungeon and the Farplane's core is also just two screens of tasks before you have reached the platforms to Vegnagun.


Also I am missing at least Banora and Above Midgar/Inside Omega in the poll.

My choice would be either the Rift, Above Midgar or Orphan's Cradle. Memoria is also not bad but I don't know.

The Northern Cave would be cooler in my opinion if there were more of the style the last section shows Inside the Planet.