I am saving Kain's for the last. I have finished 5 trials so far (including the twins), this is my second time through the dungeon with 4 new characters, and I just completed Rydia's trial. I actually quite like all of them though, my favourite trial so far was probably Edge's, and that crazy castle to work through. The Twins was also a lot of fun, it reminded me of Daccat's dungeon in Skies of Arcadia, which is one of my favourite dungeons ever in an RPG. Cecil's trial, just think like a Buddhist and you get the Lightbringer sword (which is a pain in the ass to have fighting the end boss of Rydia's trial). Yang's trial was strait forward, Meteor every single battle, and you're set =)
So my first part through: Cecil, Palom, Porom, Edge, yang; all complete. My second party through, Cecil (you always have to bring him), Rosa, Rydia, Edward, and Cid. So Kain will be the last one to go, as a part of my final party.
EDIT: I totally forgot that I cleared out Edwards trial too, it was my least favourite one. It was very short, and very easy.
PS. You KNOW the dungeon is a good one when you have random chocobo fields, towns with all the luxuries of a typical FF4 town, libraries filled with scholars, castles with attendants, and other sorts of settlements sitting right in the middle of the dungeon =P
It isn't just the trials that are good, but the actual dungeon in which all the trials are located, I really enjoy it.
I really recommend this version of the game to anyone who even remotely liked the original. Anyone who knows me knows that I really disliked the original, but I am absolutely loving this new final dungeon.
-Insert Inspiring Quote-