I'm chiming in late but I must disagree with my good buddy Rob. I think it is better for the front paddler to get in first. That way they can be in full control of the ski and even help to steady it by paddling forward slowly while the rear gets in. Also in a learning situation, often the rear paddler is less experienced so it makes more sense for the front paddler to mount first.
Note that it may be difficult for the second paddler in to use the side saddle method.