If you're already using Team system and need a digital tool for handling your backlogs, I would recommend using Scrum for Team system. The work item definitions are clear and really useful. The help website (www.scrumforteamsystem.com) gives you all the information you need. The only thing I really missed from start was a good dashboard which visualized the sprints. By installing EPISERVER's Scrum Dashboard from Codeplex, I had what I and the team needed.