the best ai is variant from person to person... aromasin is the strongest being a suicidal inhibitor but that doesnt always mean its the best... for people that just never have estrogen issues, aromasin can be too strong for them and crush their estrogen... more often than not, people are more estrogen sensitive and do need it over arimidex but there are people out there who have to go with arimidex and/or prefer it.. i would generally say to start with aromasin your first time and see how you react because it is definitely the stronger of the two...