Well I know all 3 versions quite well. You can't buy the original anymore so its not really worth discussing. The major difference between the RS4 2 and 3 are that the RS4 2 (and RS4) is Belt driven and the RS4 3 is driveshaft. There are alot of other differences like the chassis size/thickness but most of the parts are still the same between the RS4 3 and RS4 2 and even the RS4 original.