I don't think there is a definite best practices guide (yet). But, one of the important load-balancer requirements for Splunk SHC is persistence. Each user session must go to the same search head for the duration of the session. Clearly F5 allows for many types of session persistence, and some work better than others.
I would SUGGEST you try cookie persistence. My test indexer here sends a session cookie named session_id_8000. I would suggest checking to see what the name of the cookie is that your SHC returns and then configure the F5 to use that cookie for session persistence.