You want your subject to be small in the picture. That's the whole point of taking a group shot. There are two ways to accomplish that: you can use a wide angle lens, or you can increase the distance to the subject.
Generally wide angle lenses will give you a greater depth of field (at the same aperture), and will tend to magnify closer objects more than distant ones. Thus, you can generally get less distortion at a longer focal length, but you may find yourself too far away from the group to communicate with them.
Here is a group photo taken from a mountaintop of a fairly large group. I used my 10-22@10mm for this shot, since I could not back up any further without going down the other side of the mountain. This represents an extreme case, but note how bigger the people in front, and especially on the side are. The close people were about 7 feet away from me.