Acrylic is better, especially for the removable section, even if you decide on glass for the remainder. Polycarbonate (Lexan) would be the choice if it was curved because acrylic doesn't take a bend without heating in an oven. Acrylic is more brittle but will not scratch as easily as polycarbonate, and is not as vulnerable to UV degradation. Polycarbonate sold as "UV resistant" is a laminated product with a plastic coating that scratches even more easily than standard polycarbonate.

Polycarbonate will become cloudy over time from UV (like old car headlight lenses) but acrylic will eventually craze. Acrylic will hold up up longer than polycarbonate before showing damage from UV. If you go with polycarbonate you should also make a snap-on sun cover out of sunbrella. My windshield is curved polycarbonate -- here is an image showing the sun cover attached. I always clean the windshield gently with clean microfiber or towel rags and fresh water before attaching the cover, so salt crystals don't form beneath and cause scratches.