Get real world comparisons by calling suppliers in your area and getting estimates. It varies by region and these are very regional forums. Some can tell you of their experiences concerning price differences which might give you some idea, but best to go local.

Just my two (or three) cents.....

We are doing a remodel/addition of a 1930s dutch colonial in Norfolk, VA. Initially, we had selected Hardie fiber cement. Seemed to be the most available in our area, and seemed to be a decent looking product.

As we did some more research and discovered the other brands, we switched to Nichiha mainly because at the time it was a thicker material than Hardie (I believe Hardie has since introduced a thicker line to compete). We thought the thickness would be more architecturally in line with a 1930s house.

And, to take things one step further, we are installing the siding ourselves and have found the thickness actually makes the installation 'easier' -- you have less snapping, and one person can carry the pieces. (Plus, carry a few pieces a fiber cement and suddenly you don't have quite the need for the annual gym membership!)

From a price perspective, the two products were pretty much a wash. I think actually for our job nichiha priced out slightly cheaper, but we are using a combo of smooth (nichiha was a little more) and shake (hardie was more), so I'm not sure this is the norm.

Finally, and I am only basing this on a comparison to hardie's hardie-soffit which we are installing as well, the nichiha just has a better/more substantial feel to it. Truthfully, hardie feels like a reinforced cardboard. Nichiha feel more like cement.

Best of luck!