One is less powerfull than the other, if that makes sense.
Nolvadex is the next one.
Here is the list
Letro, Arimidex, Aromasin, Nolvadex
The are all basicaly the same, but more powerfull as you get closer to letro for example.
I like arimidex and the way it deals with E2 conversion enzime vs blocking.
I would rather prevent than block, block does not get rid of the estro, just blocks recepters.
I would run .25 arimidex while on PCT. When you stop your test, there comes a point where you end up with more estro in your body than test, this is the point that they call REBOUND.
Your testis are not back online and you have WAY too much estro in your body, it causes bad acne and a whole other whack of issues like depression and what not.
If you can keep your estro in check while taking your HCG (or giving your body time to adjust) then you will be much better off.
I still like an old school taper to a very low dose (125mg) then come off myself. The body does not have as far to adjust if that makes sense. However the old school taper takes about 6-8 weeks to deal with.
If your only on 125 mg test, its a much smaller difference for the body.
The trick here is to get your testis back online as fast as possible.
Hope all this rambeling helps.