How do red, white, and russet potatoes differ?

Red potatoes contain a higher ratio of water to solids than the thick-skinned, oblong russet (brown) potato. Red potatoes also contain more sugar than russets and have a sweeter flavor.
 
Due to their crumbly flesh, the russets don't hold their shape well after they are cooked. As such, they aren't well suited for casseroles or potato salads. However, their light, fluffy texture makes them ideal for mashing or baking.
 
Red potatoes have a thinner skin and are ideal for boiling and steaming. They are frequently used in potato salads.
 
Similar in shape to russets, white potatoes are known as boilers because they hold their shape well when cooked this way. They are frequently used in casseroles, soups, and stews.
 
 
Source(s):
Reader's Digest "All About Potatoes"
Simplypotatoes.com "Frequently Asked Questions"