What is the best place to apply an irule in the APM environment

I would like to know what is the best place to apply an irule in the APM (Virtual Server or VPE)? 

My idea is gather some information from the session and save all of them in the local log to be parse by the SIEM tool. The field that I am interested in are the following:

Session ID , User , Client IP , Virtual Server , Start Time , Expiration , Profile Name