The People app
Developers have built several third-party Windows 8 Twitter clients, but you can’t really use any of them. Twitter restricts third-party clients to a maximum of 100,000 users and the Twitter apps for Windows 8 have hit this limit—unsurprising, since the official Twitter client for Windows 8 isn’t out yet.
Unless you were lucky enough to grab Metrotwit or Tweetro early, your best bet is the included People app. It’s not the best Twitter client, but hey, at least it allows you to send and view tweets. Alternatively, the Tweetro app recently reappeared in the Windows Store after a brief hiatus, but now it carries a $9.99 price tag that seems steep when you consider an official Twitter app is slated to show up in the next few months.