Ester-C is easier on the stomach. Use the ascorbate form of Vitamin C not ascorbic acid. The acid form is more likely to upset your stomach, is poorly absorbed, and must be converted in your body to be used. Taking higher doses of ascorbic acid can cause acid buildup (acidosis) and can increase your risk of osteoporosis. The best forms are magnesium ascorbate and calcium ascorbate. I prefer the former.