If you log into the mobility gateway you can issue "show snmp trap-list" to see the available traps and their status. You can key off of some of those for monitoring. I think "best" is going to be subjective based on what you care about, but things like "coldStart", "warmStart", "linkDown", "linkUp", "certExpiringSoon", "certExpired", "fanFailure", "lowMemory", etc. See the list for all options.
Also see - https://community.arubanetworks.com/discussion/arubaos-8x-mib-guide
You can do an SNMP walk on the gateway to see other available info like OIDs.
snmpwalk -v2c -c <community string> <gateway ip>
------------------------------
Michael Haring
------------------------------