Have you ever heard of colloidal and ionic minerals? The next to the smallest is now called Angstrom. It is the most absorbable calcium molecule, while coral calcium is better than calcium carbonate, Angstrom size is the best. Let me give you an example. Would you rather shove a loaf of bread in your mouth, one slice at a time, or one bite at a time? While shoving the whole loaf in your mouth, you will get bread, but the rest of the loaf will be wasted, as you can't get it all in your mouth at once.
Kevin is right coral calcium is the best of the solid calciums, because it is plant derived from the coral plant, but his studies must have not included liquid calcium, which is the best of all calcium.
I really feel like the liquid calcium I take is a very good one. It is Angstrom Liquid Calcium and I get it through http://healthshop101.com