I was wondering if there is a general recommendation about the installation of HBase masters according to Hadoop Namenodes.
You should set up HBase master on 3 nodes with zookeeper for high availability. In production you should not run any thing on the nodes where namenodes are running.
Namenode is the most critical component for HDFS, if it goes down nothing else is usable on the cluster. So, it will be good to have completely separate nodes to mitigate issues as much as possible.