Yutai's suggestion for your choice:
a.Right-Angle Prism with AR Coating on the hypotenuse if you wish to use your prism as a retroreflector and you want to reduce surface reflections over the specified wavelength range of the coating.
b.Right-Angle Prism with appropriate AR Coating on the legs if you wish to use your prism as a 90 degree reflector and you want to reduce surface reflections over the specified wavelength range of the coating.