That all depends on the person. Some people don't use an AI at all because they have no estro sides. Others, like me, start taking them from the beginning just to make sure there are no sides. Aromasin is stronger than armidex, but has a shorter half life. But either work just fine. I personally use Aromasin 12.5 mg ED because of this.
What do you think about Enanthate and EQ vs. outlined Sust and EQ for my cycle based on my stats and what i am looking to accomplish?