They both work fine, they are just dosed differently based on potency and half life. Aromasin is more health friendly and there can be no rebound. Arimidex dropped my HDL from 90 to 70, and raised LDL 15 points. That's at 0.5mg every 3.5 days on 140mg/week (currently) E2 is at 11, a little low. It's strong stuff. Aromasin has a ton of benefits and is neutral on everything else, but it's expensive, and you'll have to private purchase (TRT Docs don't even Rx it). 12.5mg every 3.5 days worked for *me* at 100mg/week, E2 was at 13 IIRC, but I'd have to check.