SQL Server 2012 - 3 SQL clustered instances - one default/ two named instances - how assign/should assign static ports for named instances

We have two physical servers hosting 3 SQL 2012 clustered instances, one default instance and two named instances.

The default instance is using port 1433 and the two named instances are using dynamic port assignment.

There is discussion about assigning static port numbers to the two named clustered SQL instances.

What is considered best-practice?  For clustered named instances to have dynamic or static ports?

Are there any pitfalls to assigning a static port to a named instance that is a cluster?

Any help is greatly appreciated