If you're looking for a team-oriented Twitter tool, here's some must-have features to consider:
Multi-account support. The ability to log into and manage multiple Twitter accounts from a single application or tool.
Multi-user support. Putting the team in “team tools,” multi-user support lets multiple tweeters work in the same environment and, if necessary, be individually identified.
Statistics: Once you start pumping multiple Twitter streams, lists and contributors through a single app, the available statistics and metrics to mine begin to get interesting.
Scheduled tweets. When managing multiple accounts, at times, it's easier to batch social media work, then send it out to the world over time.
List management. If you are managing multiple accounts while trying to track different communities of interest via Twitter lists, good list management creation and tracking features are a must.