I never liked the Saint Seiya manga much. The anime just does everything better. And the manga's art is kind of, well, terrible. But since only the manga was released in English, it's not like you have a choice anyway.
The Isaac episodes were great. More Hyoga backstory is always good.
Prepare to be blown away by the first set of Hades OVAs too (I remembered the first time I saw them like it was yesterday, I was in complete awe *_*). And then be prepared to be sorely disappointed by the rest