Ice Dragon: 3/5
Their low HP compared to the other dragons counteract the fact that there's four of them

Red Dragon: 5/5
His attacks were ridiculous (especially his one hit kill strike and finishing with Ultima)

Blue Dragon: 2/5
Though he inflicts status ailments on himself and passes them onto you, it's not as bad as the tricks the other dragons have.

Holy Dragon: 4/5
He did Heartless Angel and that light attack a bit too much for my tastes

Black Dragon: 2/5
You summed it up quite well.

Gold Dragon: 3/5
It was a bit tricky with his Constant Runic ability, but he's manageable if you prepared well for the battle.

Storm Dragon: 3/5
As long as you defeat him quickly once he reaches his critical stage, he's manageable.

Earth Dragon: 2/5
My best friend here was Angel Wings (you can't be affected by 50 G's that way).

Kaiser Dragon: 3/5
Though that may be due to me using really cheap strategies like 5 Ultimas with the Celestriad and Soul of Thamasa as Relics and Quick with Cyan's Bushidos.