There are several types of screen surfaces, with different attributes designed to accentuate the projected image. For the great majority of users this choice will come down to two: a matte white or matte grey.
The advantage of the matte white type surface is high gain (greater return of reflected light) and wide viewing angle. Most screens will have this type of surface. With the introduction of high brightness LCD and DLP projectors, the use of matte grey has the advantage of greater perceived contrast but will typically have a lower gain and tighter viewing angle.
Your choice will be dictated largely by your projector selection, seating arrangements and how much you can control the ambient light in the room.