router-id in RouterOS is selected as lowest IP address of the router on the contrary of Cisco, where this is the highest IP. But, I have some related questions:

1. Cisco prioritizes loopback over other interfaces, what about RouterOS? I know how to define router-id manually, but I am just wondering about automatic assignment.

2. If I manually set router-id's of all routers, how this will affect DR and BDR assignment if I keep all priorities to default value? Will it use highest or lowest router-id? Or is it affected by router-id at all or just by priority?

3. Where to set router's priority, /routing ospf interface or /routing ospf nbma-neighbor?

For best results create a loopback by creating a bridge with no ports assigned to it. Give that bridge a loopback IP and use that as your router ID.

Router priority determins designated router and backup designated router. Once ospf interfaces are up and running open the dynamic interface and copy it to make it a static interface. You can then change router priority. Highest number wins. You can also use a 0 if you dont want that interface to be part of the election.