Tempered glass is the safest. It breaks into tiny pebble-like pieces, while standard glass breaks in sharp serrated debris.  Single pane windows have just one pane of glass. They offer less insulation protection from heat or cold.  Double pane (or insulated) glass contains a sealed air pocket between the inner and outer panes to resist the flow of heat. Find out if Low-E glass if available.  Think about how you plan to use your sunroom, and choose the type of glass that is most appropriate for your needs and budget.