You should try Bran Austin at Barrett Baseball/Hitters Park. My son has been going since 2008. He graduated this year and has a scholarship to play baseball in college. Here is the address and number: Barrett Baseball 1595 Redi Rd # 400, Cumming, GA 30040 (770) 889-4505
Matt Pritchett (Denny's son). We went to Matt almost weekly for 3 years while my son played in high school. We had switched to Matt and it was by far the best decision that we could have made. What I liked most with Matt was how well he related to the kids and aside from hitting, he teaches the kids to think and make adjustments. It's alot more than just going in for 30 minutes and taking a bunch of swings.
I second Chris or Nick at Hard Knocks Baseball Academy, right off McFarland Road. 770-754-4060. I also recommend REPS outside of just lessons and practice. Lessons are great, but if the lessons learned aren't repeated.... HK is a great place for those reps as well since it's rarely crowded.