You can't go wrong with either of them, I have built machines using both. The 12 PWM is larger, by about 1/2 an inch in depth. I think it is slightly more quiet, although both are very quiet to begin with. With 6 year warranty you know they have built a quality product. The 12025 has a longer connecting cable and is a little heavier. Other than that, they are pretty close to the same.
Here are the links, in th elisting they actually list the 12 PWM as slightly more quiet (very little). I believe that is correct.
12 PWM
http://www.arctic-cooling.com/fans2.php?idx=111&data=2&disc=AF12025 PWM
http://www.arctic-cooling.com/fans2.php?idx=108&data=2&disc=JD