Pokemon has Standard and Expanded events. There are also sealed prerelease events.
This season the larger events were regionals and they were Expanded, but everything else was basically up to the Event organizer.
If the question is what gets the most people? the answer is simple, whatever the format is for the next big event, ie states, regionals, nationals or worlds.
There is no "average turnout" - Saint Louis Regionals almost had 1000 people and other areas like Kansas only had a few hundred. So it varies by area and event type.