We are usually at MDRF most weekends. I usually make it there for about 15 out of the 19 days. Of course, if we do Days of Knights, there's a weekend I certainly won't be around.
I don't make it to PARF every year, but sometimes I plan on going on the opening weekend, since it usually opens the weekend before MDRF does. But later in the season can also be more appealing, since August on a paved faire site can make for some unappealing temperatures.