What materials are used for aircraft windshields?
On light aircraft, acrylic windshields have been the norm.  On higher speed aircraft, glass and laminates are used, particularly with heated windshields. The laminates may use polyvinyl butyral (PVB) is tough and ductile which enhances mechanical properties and impedes shattering of glass layers and the transmission of cracks from one layer to another.

Layered products may have various coatings which affect transmission of light and RF, reduce reflectivity, include elements for heating. While I do not know of an aircraft application, it is common in automotive for layers to include radio antennas.

Glass is an amorphous, non-crystalline material and acrylic plastics and glass have very different properties.  Glass tends to shatter with sufficient impact. However, glass tends to have high resistance to temperatures that subsonic aircraft will normally encounter. Glass also retains good clarity properties over the operational domain of subsonic aircraft. Acrylic tends to be pretty shatter resistant, although I know a turkey vulture which proved otherwise (grin). Acrylic is more suspectable to abrasion and scratches, and therefore requires cleaning and maintenance considerations which glass does not.

It really depends upon the type of aircraft and the design criteria, which include the operations, temperature, heat requirements (ie hot windshield for de ice), weight considerations, EMI considerations (coatings, etc.) and so on.  

Both materials have been in use for a long time.

So what kind of aircraft are you talking about?