For strictly photography, i agree with what Greg the King says above as long as the acrylic, or glass for that matter, isn't gouged. But in my opinion post-processing evens out the playing field between low iron glass and acrylic.
But, i've found glass is much easier to control streaks of light from a flash than acrylic. Acrylic produces a ring of light pattern that can become difficult to manage if you're not used to it or right up against the pane. Glass is much more managable to allow a little more variety in lighting creativity. Just my opinion, of course.