Well i guess it depends what you want. They have the same screen size, approximately same weight (the 520 is slightly lighter), same camera, same RAM, and they both take SD cards. However, the 520 has 8GB of internal storage, whereas the Ascend has only 4 which has been problematic for some users with the HTC 4S which also has 4GB. Also, Nokia is fully invested in WP so more exclusive apps etc and im assuming since its Nokia its much more durable (not sure however..). On the other hand, the Ascend has a front-facing camera, whereas the 520 doesnt, and has a slightly better processor 1.2GHz vs 1.0GHz but I doubt that will make too much of a difference since the 620 is reportedly running just fine on a 1.0 GHz.