Here's a great map of the loops. The river is on the right. https://www.parkrangerjohn.com/wp-content/uploads/2019/12/Gros-Ventre-Campgroud-Map.jpg

Short answer is really none, but several sites on different loops have shorter walks to the river. For example sites 136-141 or 179-184. You can use google maps recreation.gov to see terrain and site locations. Also looks like recreation.gov now allows reservations . . . when I visited in was first-come only so when busy you just took whatever site might be available.

All the loops are similar in distance to the river. Loop A is less wooded (more open) so has more views and I find it the most desirable. As I remember, it is probably not more than 100 yards to the river.

They are all close, however you can't really see the river from the campsites. It's a short walk to the river; i think best access is from loop C (generator loop). If i remember correctly there is a pool that might be 3-4 feet deep where kids can splash.

All of the loops are aligned along the river. You’ll need to check the campground map to see which sites are closest, as there are a couple of hundred sites.

All the loops parallel the river with the sites on the southeast side of A, B,