Respectively, 303 and 303Se are cutting stainless steel which containing selenium and sulfur, the main requirements for cutting and high surface finish occasions.

 If the water in general, I will recommend you to use 304 stainless steel.
304 stainless steel is a versatile stainless steel, it has good corrosion resistance and formability.
If it is used for salt water, or some of the chemical industry, I propose to use the 316 and 317 stainless steel.

316 and 317 stainless steel contains aluminum, superior pitting corrosion resistance compared with 304 stainless steel in the marine and chemical industries environment.