Should I use SOAP or REST API?

In spite of being so much older, the SOAP API is still being considered a better choice for replication purposes. This API proves to be more stable and has a better performance especially for bigger ServiceNow instances.

The REST API works fine too. For some of the mid-sized ServiceNow instances, it is even faster than SOAP. However, it tends to time out from time to time which makes the replication process less stable and less predictable.