A lot also depends on how much you sweat and the affects your hand have on the guitar neck. An interesting fact; I moved to California from Indiana. I tend to sweat quite a bit unfortunately, and the mild heat of the midwest did not fair well on my guitar. However, once I moved out West, the dryer heat caused my hands not to sweat as much and now my strings last much longer. I also use Elixir strings all the time, and that does help.

Another thing to think about is how you re-string your guitar, how your guitar is set up, and your technique. All of these effect string life as well. If you find you are routinely breaking strings; look into all of these factors with your teacher or professional (i.e. music store employee, fellow musician, etc.)