Not sure why the camp sites at the Village in the park get mediocre reviews. Yeah they don't have hookups which is fine for dry camping, but the spots are level with quite a bit of grass and trees. Plus there are a LOT more sites there than in the parking lot with the hookups and you can use your generator in most spots. The dump and water fill-up station is nearby too and the store is within walking distance.
Camping in the Basin is nice if you have a small RV, but since they changed the traffic patterns and reduced the number of spots for generators it has become a real hassle to camp there in an RV. I've been told the Head Ranger wants it that way since he wants to encourage only tent campers in the Basin.
Cottonwoods is nice, but a long distance from most other things. The camping area is level and grassy with some trees, but it's a no generator area.
However, Big Bend is a pretty primitive park and most things are a long ways away. Make sure you plan for that with your groceries and such. Plus 4-wheel drive is strongly recommended for visiting many areas or traveling the backroads. It's really a park designed for the 4-wheeler, hiker and bird watcher.