So you've used both and prefer arimidex? Everything I've read says aromasin is by far the better of the two. Maybe you had some crap stuff?
well I also come from a context where I'm extremely lean. My natural low e2 (before injecting T) was 10 pg/ml. In that context aromasin seems to nuke me no matter how small the dose. Arimidex is in my experience far less powerful and allows me to hit the right spot with more ease.
I've read similar reports from other TRT forums. So I think they are both close.
I'd never take Letrozole though.