Cold-roasted dark roasted coffee will be the least acidic. This will help protect your stomach and teeth. If you want an even less acidic option, try to find coffee beans that are low in acid. Basically, the temperature at which the bean is roasted affects the chemistry of the coffee infusion.
Therefore, regular iced coffee that was prepared with a hot preparation method and then poured onto ice will be as acidic as any hot beverage. According to Thomas Jefferson University studies, cold beer often has a slightly higher pH than hot coffee. I'm not very sensitive to acidity, but cold beer is great for keeping me from having stomach problems, so that's amazing. The point is that brewing coarsely ground coffee in fresh, cold water for 24 hours can help balance its acidity and can also distribute lipids more evenly.