Stainless, IMO

A cast iron sink is what we always suggest to our clients.

What is the style and color(s) of your kitchen? What color are your appliances? Having said that, I like my stainless steel sink, undermount.

Here is a discussion on this not too long ago.
https://www.houzz.com/discussions/stainless-sink-or-white-cast-iron-dsvw-vd~687822

I believe the counter top is the key to selecting the sink. Do you have granite? What are the other appliance colors?

That depends on the color of your counters and appliances. If they're cool colors and stainless, go with stainless. If they're warmer and your appliances are not stainless, you can choose fireclay, granite, or even copper.

maintenance is a huge consideration. s.s. will scratch over time so if you like pristine, you may not like this option. cast iron is a great idea but can be costly if budget is a consideration and inferior lines will scuff and can have issues with wear (kohler has lifetime warranty on their cast iron). the stone composite sinks are very durable and fairly cost effective with fairly broad selection of colors.

I have stainless steel kitchen sink with black granite countertops.