I watch twitch from Los Angeles on AT&T U Verse. Within the last few months it has been stuttering like crazy (and it used to never stutter at all). I have a great computer so it is not a computer issue. It also doesn't stutter at certain times of the day.
We've gotten a lot of reports from users about their AT&T service being choppy with our CDN. Please contact your ISP about this issue, so they can collect and collate reports about their routing issues. Once they have enough, they may contact us about it and work with us to fix their routes for multiple users.