I would go to Franklin. 1) I haven't gotten to go yet; 2) Ancestors fought there; 3)That Guy was there; 4) That was my first donation to the CWPT, and I want to see the results! (I've been very pleased with additions in other places I've gotten to go!)
If I could only visit one battlefield, it would have to be Gettysburg, though. Like everyone's said, the commercialization is sort of unpleasant, but then as soon as you leave town, it's back to 1863--and you really can plan ahead and avoid crowds. Antietam would be me second, just because it's so unspoiled, and from what I've heard, Shiloh would be a close third.....maybe this year. I'm hoping to attend the CWPT teacher institute at Franklin and mosey over to Shiloh as long as I'm in the neighborhood. And maybe I'll finally make it to Vicksburg after trying for many years!