Written. As mentioned above, to skip the useless stuff and anything you already know (which tends to be a great deal as you get older).
In addition, one of my main reasons to prefer written tuts over videos, is that nearly everyone doing a vid-tut where they talk over and present their “work flow” is really really bad at it. Bad as in; The pain and discomfort you experience while making the tut, is directly conveyed to the viewer, in addition to the fact that you are likely wrong, and do thing in a backwards way.
Regardless of the fact that it might be a free tut, the pain and discomfort is there anyway, listening to someone screech and mumble while they nervously miss click and occasionally pause to think about their mundane existences. Plus, you wasted precious time.
(Ok, this might be a bit harsh and was ever so slightly over-dramatised).
In any case, a well thought out and presented tut is superior to a “hey I just found this out, and I think I’m the only person alive that did, regardless of what google tells me” type tut that saturates the web these days, regardless of medium. I recently tried reading though the mad rambling of some Frenchman regarding realtime shaders and behaviours of materials in the real world, and as time went on I started to question my sanity. It was appalling, and really long.
While never having made one my self, I think the work required to make a proper good tut written is less, and lets you edit it later on if you notice mistakes etc, while making a proper vid takes more time, more rehearsal, and once its out there, you’re stuck with it unless you remove it completely.