Unlike framed showers, frameless shower glass must be thicker to achieve proper support and structural integrity. The two most popular sizes of shower glass are 3/8 inch and 1/2 inch.
Anything less than 3/8 inch will not have the structural integrity to last and will be wobbly upon opening and closing the door.
When the door is hinged to the stationary glass instead of the fixed wall, 1/2 inch glass is typically required. Shower glass also comes in several different styles including clear glass, frosted glass or privacy glass and rain glass.
The type of glass chosen is mainly a matter of preference or aesthetics. There is no structural benefit to the different styles as they will all be tempered (safety) glass.
Tempered glass is as a result of a special manufacturing process that makes it stronger and changes how it breaks. In case of breakage, it fragments into numerous small chunks that are not as hazardous as normal glass.
Also, see Shower Guard Protection