Here's a previous thread on this subject:

Here is a link that might be useful: Stainless vs. cast iron

I have used both, and I prefer SS, because the cast iron (white) always marked when metal rubbed against it. It was a two hole, 8" deep for both which was nice, but the divider was at least 2 1/2-3" wide. Since it was my second sink for this cabinet I had to go with a drop in, and the edge around the sink sat up higher than I liked. We have recently replaced it with a SS which is also a 2 hole, but the large side is 19" x 16" (I can fully immerse my large roaster/20-22 lb. turkey size)and it is 10" deep with a grid, the smaller side is 14" x 16" and also holds a lot. The divider is only about 1 1/4"-1 1/2". I have been using the new sink for over 3 mo. and I highly recommend it.

Jane

I think cast iron is prettier when kept up--which takes a little more effort than SS. But I'll always buy SS because I'm clumsy and break things on cast iron (and fireclay). SS has a little bounce to it. It doesn't look dirty even when it is. It'll take all kinds of abuse and recover nicely. I'm just not careful enough or clean enough to keep a cast iron sink looking its best, but it was the high mortality rate of coffee carafes that really converted me.

And as Jane points out, you do get more usable sink space because the material is so much thinner. It can make a difference if you're dealing with a smaller kitchen or sink area.

Like Fori said....Stainless doesn't look dirty even when it is. I LOVE that about it. I love cleaning my new kitchen. I keep the appliances clean and polisned, the the granite spotless. The sinks....I just rinse them out and they look wonderful. I guess upon close examination, you may (will) see water spots, but they are not at all noticable and don't bother me in the least. Keeping the dark marks off a white cast iron sink drove me nuts though!

If you've ever accidently knocked over a wine glass in a cast iron sink, you know that the glass is history. Often, the same accident in a stainless steel sink ends in a happier result, the glass survives. Stainless steel is much more forgiving. In all likelihood, you'll find that you end up with fewer chips and dings, too.

I'll buck the trend and report that I had a (Kindred) stainless double bowl in my last home and really disliked it for the endless water spots that I was forever polishing away. I thought it looked dirty all the time even when it wasn't! So, your mileage may vary. :)

If you do get water spots with your water supply, SS or anything dark will show it for sure. White cast iron would be the way to go if spots bug you!

I love SS sinks. easy to care for, no worries. I have 'good' water (no need for water softeners and no spotting) so spotting has never been an issue. Even if there were spots, don't know if I would ever notice them - it seems like my sink is always wet because i'm working in it!

A high quality SS sink is a nice sink. Typically a 16 ga 18/10 made of 304 SS is a bit more than you need, but so is granite. 18 ga is ok, but make sure the granite company is using undermount sink brackets, not the mounting brackets that come with the sink. Have you considered a granite composite sink?

Here is a link that might be useful: Granite Countertops