In general it does not really matter, I would use 16-23 or 1 or 3.
The output and content will be always the same, its just tagged with a different facility.
Its more dependent on how you configure your syslog server and how you want to postprocess it.
You can use for example 16 for all your VCS and 17 for your MCUs and then generate specific log files
like /var/log/mcu.log and /var/log/vcs.log.
You can read more in your syslog server docu or on the net:
http://en.wikipedia.org/wiki/Syslog
http://tools.ietf.org/html/rfc5424