I lived just 1hr20min from Chatt Hills, so I've shown and schooled there in different conditions. I've also shown at the River Glen Aug show many times. I would pick RG over CH. I think the footing is better, the weather is better, the stadium courses are really well designed and the atmosphere is more gracious. Oh, and the food at RG is better. In fact, RG is one of my favorite venues.
...take your chances. None better than Chatt Hills for doing all that is possible for making mid-summer footing as good as it can be...now read into that last statement. If there's been no rain - the Chatt Hills folks will be aerating rock hard ground. Same for River Glen - and more than likely, in July, count on HEAT (mid-90s or above) and humidity. If you are somehow blessed with less heat and humidity - count your blessings. You decided to event in the summer, you obviously have a good brain and a good reason. Kick on or kick back and CHILL!
~ it no longer matters what level I do, as long as I am doing it..~ with many thanks, to Elizabeth Callahan