You Basically have 2 Aromatase Inhibitors.
Arimidex and Aromasin.
Arimidex has been around for a while, and most TRT Docs still prescribe it.
Personally, I see 2 Problems with it.
1 ~ if you stop taking it suddenly, without reducing the dose over a couple weeks, Estrogen Rebound can occur.
As it only Binds to the Aromatase Enzyme while you are taking it.
2 ~ in Clinical Studies, it Negatively Impacted Cholesterol Values.
Aromasin is the Newer one, and it's a Suicidal Inhibitor.
So it makes a Permanent Bond to the Aromatase Enzyme, so only New Enzyme Activity can occur.
And in Clinical Studies.
It either had No Impact on Cholesterol, or showed a Slight Improvement in Cholesterol..................... JP
P.S.
There's also Letrozole, but I would Never Ever use that for a Cycle.
It can Crash your Estrogen very quickly, which isn't what you want during a Cycle, as you need some Estrogen for Gains.
I would only use it for Gyno.