If enamel over cast iron chips, you see cast iron, if a fireclay sink chips it is the same color throughout. Both are great sinks though. Keep in mind, installing a fireclay sink takes some finesse, they are not perfectly flat on the bottom because when they are fired their shape distorts.

which do you think is more likely to chip, cast iron or fireclay?

I don't think you would have a problem with either of good quality. Kohler makes great cast iron sinks, I've installed a Rohl fireclay sink and it seemed very well made.

I'm really inclined to choose the Rohl fireclay, but I'm worried that the kitchen company I'm working with won't like it because they need the specific dimensions of the sink when they build the cabinets and I've heard that there's some variation in the actual dimensions of fireclay. Any ideas about how I might get around this problem?

They will just have to cut the front panel out on site, probably belt sand it a bit, and build a platform for the sink. Definately an extra charge to do that.

Do you think its worth it? Another problem I have is that I want a 10" deep sink and I haven't found a kohler farmhouse more than 8 or 9 inches.

That's a decision you have to make. Needs and wants, which one do you normally choose 8-)

You're right... Thanks for your help!

No problem, if you go with the Rohl, get the basin rack that goes with it.

With respect o the depth of the sink, farm hues sinks are typically under mounted effectively providing 3/4"-1 1/4" of additional depth depending on countertop material. Pair the sink with a high arc faucet and you should have a winning combination.

Thanks for this!