If you need to prepare mashed potatoes an hour or two ahead of time and would like to keep them warm until it is time to serve them, place them in a slow cooker on low or very low heat. They will still be hot and fluffy when ready to serve.

The best potato variety to use for mashed potatoes is the Russet potato because of their high starch content or Yellow potatoes because of their buttery flavor.
Potatoes come in all sorts of different colors, shapes, sizes, textures, and tastes. In fact, there are about 3,000 potato varieties! Here are some of the basic categories and what they are best used for.
Russets, the most widely used potatoes in the U.S., are oval in shape and have a brown skin and a white to off-white flesh. Russets are high in starch and have a light and fluffy texture when cooked, making them ideal for baking, mashing, and roasting.
As their name indicates, red potatoes have a rosy-red skin. These potatoes have a smooth, moist texture and hold their shape well, making them well-suited for boiling and steaming. They also taste great roasted.
Red potatoes that are harvested immature are small, low in starch, and have a fabulous flavor.
These versatile, all-purpose potatoes are oval in shape and have a light tan-colored skin. They have a somewhat creamy texture and hold their shape well when cooked.
Though they are all generally small and slender, fingerlings come in a variety of colors. They are smooth, creamy, somewhat waxy in texture and quite flavorful. Fingerlings maintain a firm texture when cooked and are at their best when boiled or steamed. Most varieties also taste good baked.
With dark blue or purple skin and lavender, white, or sapphire-colored flesh, these potatoes are some of the most beautiful potatoes available. These potatoes have a slightly nutty flavor. They hold their shape well during cooking and work great for salads.
Yellow-skinned potatoes are dense and creamy textured with a buttery flavor. Yellow potatoes are well-suited to steaming, baking, mashing, and roasting.