Acrylic and PMMA refer to the same plastic: polymethyl methacrylate. Plexiglas and Perspex are brand names also used as general terms. A different name does not automatically mean a different material.
Look at the variant behind the name
Acrylic comes in transparent, coloured, matte, mirror and other finishes. Thickness, surface and engraving visibility differ between products. These properties matter more to a design than whether you call the material acrylic or Plexiglas.
Cast or extruded
PMMA can be manufactured in different ways. Cast and extruded acrylic can differ in thickness variation and engraving appearance. Compare the actual product information. Read about cast and extruded acrylic for that choice.
A clear sheet is not always acrylic
PETG and other transparent plastics may look similar but react differently to laser cutting and use. If you buy a sheet yourself, confirm its actual material and composition. Customer-supplied material requires assessment beforehand.
Choosing for laser work
Use colour and finish to choose the appearance, then check thicknesses, cut edges and available operations. Transparency matters for a window; contrast and the visible side matter more for a logo.
Find current products in the acrylic collection. Read about engraving acrylic for engraving results.