It really depends upon the subject matter - we're experimenting! For Computer Science/programming education we've been pushing more towards the text/interactive exercise direction. Art History is almost all text and videos (with little interaction). Math is almost all video and exercises (no text).
This summer my kids (elementary & middle school) did the Intro to JS and Advanced JS courses. They really got hooked due to interactive creativity and video lessons. The audio narrative was really fun and kept them interested. Therefore, videos and especially the audio narrative style in Intro to JS is something I would vote for and hope that Khan academy continues that even (and especially) for CS courses.
I will definitely keep doing talk-throughs when we are teaching syntax- like for the HTML/CSS and SQL curriculum that we're releasing this week. I experiment with articles for when the teaching isn't focused on syntax but is more conceptual/high-level (including in the Advanced JS series, which is all articles).