Have done both. On US 129 over the mountain the road is much wider than US 76. Both have some turns. US129 has two true hairpins but the road is very wide at that point.
US76 also has several true hairpins and all have a very narrow road which makes the hairpins trickier. US 76 is more narrow overall as well.
Personally I feel more at ease on US129 with a long load. The large load truckers also use 129. Only you know how comfortable you feel.
Helpful hint: if you do choose 129, take I-85 to I-985 and get off just north of Gainesville, GA (exit 24). Take Old Cornelia HWY west towards Gainesville for more or less a mile. Then turn right on Limestone Parkway. Limestone is US 129. Stay with it all the way through Cleveland and on up over the moutains.
Enjoy Blairsville: it's our favorite small town in GA.
