Worlds of existence of angels:
The abode of majority of angels is in the world of Yetzira. The reason for this is because the world of Yetzira corresponds to the emotional attributes of the angels which is the highest level that they can reach in service of G-d, expression of their natural inborn emotions. However, there are select angels whose abode is in the higher world of Beriya. These angels have the unique capability of intellectual thinking and process, hence being able to develop innovative love and fear that comes as result of comprehension.
 Tanya chapter 39 [p. 51b]