We replaced an old tile countertop with nasty grout and SS sink with grey speckled Corian countertop and white Corian sink.
I LOVE...
... The gentle color of the counters and how they go with anything.
... Not having grout or any kind of seam between the sink and the counter. LOVE this!
... Being able to roll cookie/pie dough right out on the counter.
... How easy maintenance the counters are -- we've had a few stains, which came right out with a soft scrubber; usually a little 409 and you're good to go.
I'm not too sure about...
... The white Corian for the sink. We should probably have gone with the grey speckled for that as well. We keep a plastic sink liner at the bottom of the larger sink, which helps, but the white does tend to stain easily. But, as others have noted, the stains come out pretty easily, too. [It's just that you wouldn't "see" them in SS.]
I've not had experience with granite, but I've heard that it's pretty hard on your glasses/dishes should you drop them. Corian is hard, too, but seems to have a bit more "give" to it. But I might just be imagining that! :-)