Hemi-glass:  
Strongest, most surface area, longest resistance to caustic attack and HF, best tolerance of high pressure and pump hammer

Flat-glass: 
Reduces accumulation of accreting particles such as recycled pulp.  Less prone to impact breakage during user handling.

Flush Tip:
Easiest to clean, best resistance to fouling and accretion, least protection from breakage.

Notched Tip:
Best compromise between glass protection and ease of cleaning.  Most popular configuration.

Recessed Tip:
Greatest protection against breakage.  Best for clean processes that do not require aggressive cleaning.