I've tried a sheepskin mitt but it didn't last long. Now I use a microfiber chenille mitt from DI (looks like they don't sell it anymore) and it has been working great. I don't use it AS a mitt though, the liner material disintegrated after one use.
On one of the detailing sites I visit there was a thread likethis and the best for washing the car was a grout sponge. It was been sold at lowes for 1.50 , Ive bought 20 and havent used anything else since.