It depends on what you plan to do.
Summer and fall seasons are the best if you want to experience Gatlinburg in all its glory. The summer sun is perfect for the outdoors, while the fall foliage amplifies the area’s beauty. The same reason why it’s heavily flocked by tourists around this time.
But to avoid that, you can visit around September, when the fall season is just sneaking in, also off-season for Gatlinburg, before tourists come flooding in again by October, when fall is at its finest. The spring season (March-May) also has the thinnest crowds.
Winter is best if you love the adrenaline-rush playing through the slopes of white planes.