Potatoes vary in their starch content, skin thickness, and reaction to heat. Some are great if you want intact diced potatoes in your soup. Others are suitable for mashing. - Round white potatoes are low starch and have waxy skin. They hold their shape best and will work if you want the soup to have a skin-on chunky potato consistency. - New red potatoes are similar to round white potatoes and also good if you want to show some color in the soup from the red potato skin. - Yukon gold potatoes are great all-purpose potatoes and similar to russet potatoes, are good for mashing in a soup and adding thickness.