Should I buy Duracell or a much cheaper battery?
According to tests, Costco (North American warehouse wholesale store) Kirkland store brand AA batteries are about as good as Duracell for a fraction (about 1/3) of the price. 

If both your batteries are alkaline batteries and have similar mAh rating, they should last a similar length of time with similar current draw. 

It's quite possible to come up with "advertising" comparisons that would appear to show a 10:1 advantage for an alkaline cell by deliberately choosing an application with a high current draw and comparing the alkaline cell with a cheap "heavy duty" zinc-carbon cell.