For myself it was 45-100. There were lots of great articles- The demihuman point of view and deities, The Deities of Greyhawk, Ed Greenwood's articles on Hell, articles by Stephen Iniss and Katerine Kerr. I also enjoyed having articles on games other than ADND.
My next favorite period was 171-215. I liked the articles by David Howery and John Wybo II dealing with various Native American and African cultures. I also liked the articles on Completing the Complete Handbooks.
In between, those two periods there were some really good articles such as David Howery's "Tracking Down the Barbarian" and "The Corrected Cavalier". However, the two above periods were
My third favorite period is Erik Mona's run simply for the Demonomicon articles by James and the Sean Reynold's series on the deities of Greyhawk. Unfortunately, I couldn't justify purchasing Dragon just for those articles.