We previewed Twitter for Windows Phone 7 prior to the Windows Phone 7 launch, and it's no surprise that the official application is very similar. Twitter got a head start on its app, so it fits right in with the Windows 7 design aesthetic. We found it intuitive to use. Also unsurprisingly, it has all the features for contact management, retweeting, and photo attachments that you'd expect.
In the composition window, Twitter for Windows Phone 7 has a handy feature that lets you quickly select from a list of favorite follows (@users) to save you some typing, although our favorite method is one that suggests matching users as you start typing their usernames. You can also save hash tags you use.
There are several settings and customization options, including switching among Twitter photo services and swapping between black and white themes. Switching profiles could be easier for multiple-account holders, and we weren't able to post to multiple profiles. And, unfortunately, Twitter has work to do to speed up laggy scrolling.
Twitter's offering is the better-rounded overall, but it doesn't have all the extras that you find in Seesmic, like link-shortening and triggering a camera to take a photo and upload it to a tweet. It comes down to your own preference.