Roaddking spelt it out pretty good!
i prefer arimidex on cycle- it's what I began using as an AI on cycle since and has always done me right, so I've never switched to aromasin on cycle. ( idea being if it ain't broke don't fix it)
i see aromasin is beginning to become the choice AI on cycle though and it makes perfect since for the reasons RK stated below.
some of the most respected members here prefer it. I definately make the switch during pct to aromasin.
either one of these would be a good choice and Don't think Letro wont do it too!!! Just the sides guys report back can be tough, and better left IMO for gyno, or at least to try as an AI later on in next cycle. I would highly suggest picking some up to have on hand as precautionary measure.