I believe you have to split your question into two parts because we're really talking about 2 cycles in FF history, before and after non-flying miles accumulation. No doubt the tripple miles deal stands out in memory but for sheer volume of accumulating miles, for me it was thanks to Citibank. During 1999 they launched their "Click-City" Aadvantage card. All early applicants have zero annual fee for life and earned double Aadvantage miles for the 1st year.