To prevent a rebound should I go with nolva or aromasin once I finished letro.
What's this for exactly? Were you on a cycle?
The Letro, if I recall correctly, typically crushes estradiol levels 95%+ (to almost zero), so you will NEED to be protected. This way, you'll gently allow your estradiol levels to normalize while under the protection of the Nolva and repressed by the aromasin, and then taper off the Nolva to gently allow your test levels to fall to normalize with your estradiol levels. It'll probably take a while. You may be able to get away with running the Nolva for 4 weeks. I personally have never done anything like this, nor have I used Nolva (I use Toremifene for PCT), so it is purely speculation, but I really can't see four weeks being long enough to return to homeostasis after a Letro cycle. As soon as you stop the Letro, you will have a LOT of testosterone just DYING to aromatise to estrogen as soon as aromatase enzyme production increases. You will need to control this, and I think it'll probably take a little longer than a normal PCT.
I agree with the above, I would run the nolva 6 weeks, I don't think 4 would be enough either.