SD-6 is a marginal Republican-held seat that includes the territory of HD-42 above (perhaps explaining why only one candidate filed there) plus the rest of Smyrna, bits of Cobb County connecting it to Fulton County, north Atlanta and Sandy Springs. It could very plausibly vote for a Democrat and is easily the most competitive seat, although it is unclear to me how serious any of the Democratic candidates are. I would call it a Toss-up.
I'd rate GA-SD6 Lean D. The district went 55-40 Clinton and the incumbent State Senator barely eked out a 52-48 victory in 2016. The Democratic nominee is running again, as well as a second serious Democratic candidate. With five Republican candidates running even a D v. D - runoff is possible