I've found that it's best to score the smooth side for cutting. This, whether using score and snap, or using a saw of some sort.
For the former, I find a heavy utility knife a better choice than an xacto or scalper-like cutter.
For the latter, using a fine veneer blade installed "backwards" in a variable-speed saw a good choice. This puts the teeth of the blade into the "sea" surface, so any splintering is on the back (easier to file & sand clean) side.
Truth be told, my tool of choice for the light lens sheets is a Rotozip with a laminate-cutting bit. This, however can be kind of spendy for some one who is not going to install a lot of plastic laminate counter tops--legacy of a life time in construction for me.