Alright then.
Odin vs. Raiden: This depends on what you want. Raiden teaches the amazing Quick spell, but Odin is the only magicite in the SNES version that raises speed at level-up. If you want your characters to have more speed, you might want to keep Odin. Otherwise, upgrade to Raiden ASAP.
Ragnarok sword vs. Magicite: The Ragnarok sword is the second best weapon in the game, but the Magicite teaches Ultima, the strongest magic in the game. However, it's also possible to learn Ultima using the Paladin Shield. I'd recommend the sword if you're playing the SNES version.
Another thing to keep in mind if you're playing the SNES version is that the Evade stat is completely useless due to a bug, so don't bother raising it.
I didn't know about the evade thing, Thanks Gustave you've helped me a fair bit tonight too (since I just started my current FF6 playthrough) :)