I bought both the gargantuan black and the blue, and found the blue to be higher quality than the black. I like the pose a lot better, it's more draconic and animalistic, the black looks somewhat like a salsa dancer. The blue is noticably heavier with a thicker better quality base. As for stats for 500 points side by side the blue is a hair tougher, generally +1 to most attacks over the black, and +1 to most DRs on effects. The collosal red was too rich for my blood, but if wizards is listening I'd shell out 50 or 60 for the terrasque. The wings and most of the blue dragon were very solid feeling and the whole piece just felt higher quality, although I will agree that there was slightly more detail in the black dragon.
-Pete