As jaycocamprs said above, exit 435 has a Walmart if you need anything before continuing to the campground. Either exit is good really so its up to you so take your pick.
Take the exit in Newport (see above) and stay on 321 all the way into Gatlinburg to Twin Creek. I would NEVER try pulling a trailer or bringing a motorhome THROUGH downtown Gatlinburg. I really don't like taking my truck into downtown, if I can get away from it. It's really narrow and usually crowded.
440. If you are pulling a trailer or in a Motorhome 440 is the best bet. 443 is the Foothills Parkway, part of the National Park and has couple good grades on it and a couple turns. Very pretty, yes, but do it in your car.