According to their website RS will engage more smoothly, which is what you want on the street. On the track, response time counts more and racers don't care if the diff clunks with sudden engagement.
I would get a 1.5 way diff for the street, personally.
Shuddering I'm not sure about, but I expect it would be less of an issue with the RS diff as the springs absorb the initial shock. I've heard the KAAZ diff shudders like buggery when new, but once broken in they are much better.