Dispatch'r - When a ticket gets created; you could make use of this to make updates or trigger actions for a new incoming ticket. 

Supervisor - Runs on all tickets, once a hour, based on a time based update; could be used for updates you are looking to make based on "time since" conditions, for an existing ticket.

Observer - Triggered by the occurrence of an events; to be used for triggering actions based on activity performed.


For a detailed overview refer to this solution article.