leather is easy to clean and maintain. i don't know about neoprene, i don't have any experience with it. i don't like leather cause it is hot during the summer and cold during the winter. neoprene may be better in that regard. but i'm sure there are others that are more knowledgable
I have the Coverking Neoprene. They were a necessary purchase because my son has a talent for getting anything he gets close to filthy! While not hot to the touch, the seem to hold heat in really bad. During the summer, my back will sweat in the seat no matter how high the AC is cranked. I have the gray inserts outlined in black and you can see every place my son has thrown his sippy cup and had some kool aid leak out. But that's why I bought 'em. I wanted them to stain instead of my seat. I'm sure a little Tuff Stuff will take the stains right out, but have tried it yet.
I have pics in my gallery over at tundrasolutions. Here's the link if you're interested.