I've just been playing FFVI and I've been wondering which sidequest is the most difficult(ie, Fanatics' Tower(aka Magic Tower), Ebot's Rock, finding Gogo, getting the Odin magicite(or the enhanced Odin, I forget the name of the enhanced one), the 8 Dragons(to aquire the Crusader magicite), Cyan's Nightmare(getting all of Cyan's swordtechs and the Alexander magicite) and of course, getting Mog(again if you got him in the WoB) and Umaro(and not to mention, the Tritoch and Rangarok magicite[or the Cursed/Paladin Shield], and finally the Auction at Jidoor-to get the Terrato and that other Magicite, Raiden, I beleive.)
I'm not bothering with the story sidequests regarding [spoilers]Gau's father or Shadow's past.[/spoilers] since they are purely optional.
I don't consider getting the main characters that are optional(recounting from memory: Relm in Jidoor, Strago at Fanatics' Tower(need Relm), Locke at Pheonix Cave, Terra at Mobliz[I believe you can get her to join after getting the second Airship in WoR], Shadow[betting the Striker at the Colloseum-IF you waited for him at the Floating Continent at the end of the WoB) sidequests. I see getting them as sort of a requirement to make getting through Kefka's Tower a whole lot easier(although you do have to defeat the last two Dragons there).
I personally think so far that Fanatics' Tower is the most difficult, mainly because:
1. You can only use Magic(have Ultima and Cure/Bolt/Fire/Ice/Life3 ready, plus at least 50 Tinctures)
2. Those enemies with the permanent Rflect on
3. The enemy that casts Quake and WWind
4. The enemy(L90 Magic) which casts Merton and Meteor
5. And of course...Magimaster! Cast Beserk on him, but cast at least twice-or else face death in the form of Ultima-unless you cast Life3 on somebody, that is.
I am also sorry to say I am still doing the sidequests, but with all the information about them I can pretty much post this poll, and see what other people have to say.