epic, legendary and mythic was the original intention, but there's a few things that throw that off... for example the ancient pets are all legendary because you cannot tame em now, but really when compared to some other pets their buffs aren't really worthy of the legendary status imho. Mythic is definitely the most rare, but there are some Rares that only exist due to being competition rewards, so those are actually more rare than the others...
so as all things with Mindark, it's all a bit questionable.
Current system is still sort of based on idea of when Compets existed... In a few years when mindark redoes entire system it's going to get interesting... possibly, or not...
Along same line what's better, Advanced, Basic, Diluted, inferior, second-rate, or weak extractors? If the one you have doesn't match what you are wanting to craft with it, who cares.