Have you looked at Silgranit? The light colors don't show water spots. (We had soft water in Seattle, and even so, the stainless only looked good for 5 seconds after it was dried off.)

I had no problem with the scratches in my stainless steel sink, but I hated the water spots.

We have hard water and our stainless steel sinks have held up just fine -- no deposits, no staining, etc. (I can't say the same for the granite counters, though...)

I don't think there's a "best material" -- I can list pros & cons for just about any material out there! What might be an issue, though is "color".

I also grew up with very hard sulfur water and when we had white sinks they seemed to always stain. My parents changed to a stainless steel Kitchen sink in the 70s and have never looked back.

I even notice some staining in my current white bathroom sinks, my white tubs and shower, and in my white toilets. (My parents have also had issues with stained tubs, bathroom sinks, and toilets.)

I'll be honest, water spots and scratches don't bother me...it is a sink after all! If you don't like scratches and you decide to go with stainless steel, then consider a grid for the bottom of the sink.

I think this is a case of go with what you like -- stainless steel, granite composite (e.g., Silgranit), etc.

If you have solid surface counters (e.g., Corian), then it might be best to go with the same in your sink and get an integrated sink (Anglophilia mentioned this above).

Yes - there is a lot of personal preference involved and many good options. I've always had cast iron and my new sink is a cast iron farm sink.

I have always had a cast iron sink in white. Indestructible and easy to clean. We currently have the Kohler Bakersfield.