According to http://git.io/top when it last updated last week, it states michalbe currently has the longest streak. They have a streak of 561 days as of today according to their profile: https://github.com/michalbe
But sadly that list is for people with more than a certain number of followers. I'm not on it (https://github.com/waywardmonkeys) despite having over 2000 contributions and a 417 day streak. :(