Longtime "summer tripper" who made the switch to September a few years back.

Next year:  back to summer tripping.  

Why?

Prolonged stretches of cold, ugly weather on both September trips.  Endured a hard freeze, plus plenty of cold wind and rain--for days on end.

No swimming.  Fishing sporadic (I'm no expert, but usually do well in summer).

My gear is summer-weight stuff--warm enough to keep me alive in 25 degrees, but not sufficient to let me ENJOY 25 degrees.  

Love the "no people, no bugs" of early fall, but will take a pass on the "I'm freezing my a** off, and where are all the fish?".  

Warning to new fall trippers:  take the average temps with a grain of salt.  Pack for weather 1 month later than your actual trip date.