I like the classic Samsonite. They are not too heavy to carry up stairs, have a classic design in all kinds of sizes and shapes and overall offer a good value for money. They also survive being checked in from time to time if you need to. The cheap ones don't last very long. Another advantage is that you may be able to get free repair at their stores or a warrantee for rolls etc.
Unless you're into those fashionistas' Louis Vuitton carry-ons that are out of my price range...