MetroTwit is a fairly new Twitter client and they have done a fantastic job of bringing a visually pleasing yet easy to use and powerful interface to Windows 8. It allows you to watch multiple streams simultaneously, check user profiles, update your own stream, create and manage lists, URL shortening, infinite scrolling and much more. It has a desktop and Start menu versions.
The ad supported free version supports one account (which should be good enough for most people). If you are feeling generous or want to manage multiple accounts then fork over $15US to help the developer, remove ads and enable multi-account management.