The previous answer is mostly correct.  The higher the DPI value, the better.  (600 x 600 DPI, by the way, makes no sense).  

I disagree with the previous answerer's statement about being able to see a difference in quality.  The difference between 600 and 1200 DPI visible to the naked eye; to some degree even the difference between 1200 and 2400 is visible, especially on graphics. 

Offset type -- the printing process used for magazine -- is considered to be about 2500 DPI resolution.