The best materials for suitcase holders will depend on your budget and style.
Basic luggage racks, like the ones you find in a hotel, are made from metal and woven fabric. They will be the cheapest option and will still serve their practical purpose,  however, the silver metal may look unrefined in a personal or guest bedroom.
For something a little more "upmarket", a plain wooden luggage rack will suit most decor styles. If you want something lighter, find a bamboo suitcase stand. It will be easier to move around and is perfect for a light and airy guest room.
If you want to put a luggage rack in the guest bathroom, make sure you choose one that is water-resistant. A metal frame may rust, and a wooden one may warp over time. In this case, it is best to choose aluminum or stainless steel frame or opt for something plastic.