Blurring is often used to obscure movements for tracked data. That's fine and often necessary. However, do keep in mind what the final specifications are for the final viewer. If the final video is delivered to the viewer in 720p, with low bitrate and added facebook compression for example, you may want to reconsider wether you need to add that final directional blur to your footage as most people will not see it in the end.
If you must use blurs however, try to keep it as light as possible. Effects need to work in the latest version of AE our renderfarm is running. This can mean that some blurs cannot be used.
Use "Fast Box Blur" or "Directional Blur" in projects built in AE CC15 and above. "Gaussian Blur" can also be used but is slower. If you are using an older version of AE please use ‘Fast blur’. In newer versions of AE it appears as ‘Fast blur (legacy) in the ‘Obsolete’ folder.
These blurs are currently the fastest rendering blurs