304 food grade stainless steel is not resistant to saltwater, but it is the most widely used one in  stainless steel. Besides marine application, 316 is hard too. But there would be a little bit difference between them.

To be honest, 309 filler rod would be the best material in 304L sink. Unless you need high tensile  strength or fill the sink in concentrated salt solutions with elevated temperatures, 304 will be fine. For room temperature and moderate aqueous solutions of PH, 304L is preferred, that is why it's used for all food-grade applications.

 They have been used for many years, and there is no visible difference under same conditions, 304 performs better. However, 316L is only required in some special situations, and it is more expensive.

I have four stainless steel sinks which is made a few years ago, and I didn't know there were different types of stainless steel. The sinks rusted, particularly near the drains. I don't recall if the drains rusted, but I think they did. Chlorides may cause rusting problems unless you specify the corrosion SS for the job. In spite of that, I now use one of the two sinks without a drain and occasionally sand it to get rid of the rust. I  wonder if I could shine the thing up and then coat it with a clear finishing.

I agree that a sink could easily be made to look good, that would be cheaper and easier to build without using stainless. Down the road if you move houses or switch to digital, you could just trash the sink. It's hard to scrape a SS sink because of the money invested.

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