FF6 - Brave New World

My own personal list (Top = Easiest, Bottom = Hardest):

Silver (A single Ice shield makes this fight quite easy)
Red (Similar to above, but having a Flame Shield at this point is slightly more difficult)
Green (Relic Rings make this a piece of cake, but many wouldn't think of using them, plus there are other drawbacks)
Gold (Close to the end of the game, so you'll be pretty powerful)
Purple (Not ranked easier because its attacks can't be nullified/absorbed. Not ranked harder because the armor that halves wind is pretty good)
Blue (Gold Armor/Gator Hide is outdated here, but all attacks can be defended against at least, and the elemental resistances exist)
Brown (Some non-elemental attacks, some undefendable attacks. However, some attacks can be nullified with Float, and you can save just outside the Opera House)
White (Can't hit its weakness without causing it to heal itself with Holy Wind eventually for 9999. This is the only dragon, except possibly the Blue, who is far from a save point. Uses plenty of damaging multi-target attacks and Quasar. The Holy element isn't easy to defend against either).

It does, of course, depend on where you fight them, and I went out of my way to avoid the Purple dragon by not getting Cyan first thing. Then again, the first things I did do were fight Doom Gaze and the Brown Dragon... However, I'd say that's the order of difficulty as far as I'm concerned. I have to say I'm surprised that you'd defeat the Brown/Purple dragons and then have trouble on the Silver one...