F5 Monitoring best practices for stable environment

Assuming that you are talking about health-monitors that F5 utilizes to check the servers, it depends on your application.

Ideally, keep it Layer-7 at the pool member level. Example: HTTP (GET Request). Don't use monitors at node level as this is really not required since you are monitoring the pool members at L7 and if node fails, L7 check on pool member will fail automatically.

In short, monitor the higher layer availability for pool members.