LoRaWAN us-west.thethings.network v.s. us.mikrotik.thethings.industries

I have a wAP LoRa 9 Kit and a few questions:

What is the difference between us-west.thethings.network and us.mikrotik.thethings.industries?

Currently I have my kit set to TTN Router: ttn-router-us-west (us-west.thethings.network) in the TTN Console, but it seems that if I set that as the server on the wAP I just get a log lora, error lora-dl: [TTN-US-West] Keepalive timed out. Leaving ttn-router-us-west in the TTN Console and changing the wAP LoRa server to us.mikrotik.thethings.industries seems to work.

What is the difference between the servers? Is there any reason not to use one or the other?