Obviously, the final dungeons are supposed to be hard. But which one is the most difficult of the ones you have made it to?

1: Temple of Chaos
2: Jade Passage / Pandaemonium
3: Sylx Tower / Dark World
4: Lunar Subterrain
5: N-Zone
6: Kefka's Tower
7: Northern Crater
8: Ultimaecia's Realm
9: Memoria
10: Sin / Tower of Death??
10-2: Farplane
12: ?????

I have made it to those dungeons in 1, 2, 3, 4, 6, 7, and 9. I had the most trouble in 9, but it may have been because my characters were at lower levels. Many of the battles had instant death attacks. I haven't finished it yet.