The Wittner composite (read: synthetic) chinrest is the absolute best choice on the market in terms of comfort and sizing for the majority of the populace. Because there is no porous surface in contact with the skin, the chance of developing irritation or infection from constant skin contact is reduced significantly, an issue I've seen in some students with wood chinrests.
Of medium height, it can be positioned a distance determined by the player from the chinrest to best fit their anatomy. It helps fill the crucial gap between the jawbone and the collarbone so that players are free to use less substantial shoulder rests, eliminating the bowing problem caused by having the instrument elevated too high. It is not a good solution for students needing a very low chinrest, and for those needing a very tall one the Kreddle is probably the way to go.
I have literally purchased over a hundred of these from Concord Music for students and colleagues! :)