I will call the circle on the far left of the picture #1. It can have problems because of wind that comes up the bank on the left. You cannot really see the topography of the ground but there is a pretty good drop off on that end.
To further Bill's point, that end of the pad is raised probably 20-25 feet above the surrounding terrain. I'ts fill, and the slopes of the fill are more-or-less parallel to the sides of the pad. The worst air is when it comes from the west (from the left in the picture) up the flat part of the hill, or southwest 45 degrees from the lower left to the upper right over the corner of the two hills, and off the parking lot. That's absolutely brutal even in moderate air. In those conditions there is so much turbulence that you can easily get tricked by what you feel on your back VS the secular wind direction. The is also almost always a different wind direction at altitude than there is in the lower 20-30 feet. All of them are pretty OK when the wind is from the North but tomorrow is the first time I have seen that had any velocity from that direction. Usually if it's from the North it's not too windy.
Of the four circles, generally the air is the best on circle 3 or 4 and that's where we fly the Open finals and TT. Which circle is best depends on the wind direction. I like Circle 4 in most cases but if the wind is out of the west I prefer circle 3 - not because of the air quality but because the crown of the circle is less pronounced in that direction. I have had relatively few flights on Circle 2 but either 1 or 2 is OK with an East wind. Circle 2 also used to have the Brett Buck Memorial Chuckhole, where I wiped out my prop on the takeoff roll through a big dip in the pavement over on the northeast side of Circle 2, and had to taxi around on the ground for a few laps before I cleared everyone and ran it off into the grass on the north side of the pad. That mostly went away when it was repaved. I also crashed on the west side of Circle 3 but my divot was quite unimpressive compared to some of the really good one, like Steve Moon's from 2005 and Uncle Jimby's from 08, among many others.
Brett