Acrylic (Plexiglass is a type of acrylic) is far superior in terms of UV and scratch resistance.... In the typical thicknesses use, impact resistance is not a concern. You can also flame polish the cut (or routered) edge of acrylic.
I kind of thought that may be your answer. It is no longer the case. A number of years ago that was true. But the modern formulations of UV scratch resistant polycarbonate are far superior to what they used to be. As far as practical direct knowledge, I'm still watching. However I did use polycarbonate on a boat I redid about 10 or 15 years ago and it still looks new. I also did my hatches in polycarbonate a couple years ago on my current boat and they still look brand new. Those have now spent a fair amount of time in the tropics, have traveled quite a distance under sometimes extreme conditions.
It is true you can flame the edges. I've never needed that but that is a good point. You could also polish polycarbonate.
On a sliding hatch cover, depends on where you are sailing. Since I'm in the ocean more than a lot of folk, I want the added strength of polycarbonate for any area that could be hit by a breaking wave. Don't know if you have ever experienced that - but think a thousand pound sledge hammer smashing into your hatch...
dj