We live on the southside of Atlanta and travel to the Helen/Hiawassee area often. A good route for you would be from Lagrange to Griffin to McDonough to Covington to Gainsville to Cleveland/Helen. Lots of traffic lights, but no Atlanta traffic. This is our route to the mountains.
Just to say it out loud, if you go thru Atlanta in the mid-day (about 10:00 to 3:00), it's not that bad, NORMALLY. From I-85 in Lagrange, you could take I-85 to I-285 east, back to I-85 on the northeast side, then to I-985 past Gainesville (then to Helen once off I-985).
We've done it both ways in and out of traffic. I prefer the back roads approach (off he interstates). But then I sit in Atlanta traffic all the time for work, so I try to avoid it if possible.