An interesting question, it really depends on your business and its objectives. Are you expecting people to visit your website or do you want people to visit your website?
Those two questions are important to understand, if you expect people will visit then you need to work out what is an acceptable rate of updating the blog. Once you start you will want to keep it consistent, so once a week is a nice start but even that can require discipline.
If you want people to visit your website, then creating engaging well written content is a must. Google likes text, so text is good but it can be boring and not very engaging. Especially as a start up, you want to get people to remember you, so well thought out content is a must. It is also important not to blog on the same subjects as everyone else, try to be different, stand apart from the crowd.
Audio and Video are two channels that you can promote your content off site, there are podcast and video websites that you will want to include any content you create on. This should drive you some visitors to your website if you point them to it. Try intro Podcasts and Videos for offsite promotion and then point people to the full versions on your website.
So I don't think there is any reason to focus on Print, Audio or Video specifically unless it suits your business and customers to focus on one method in particular.
Hope this helps!
Quick Answer: Start with text blog.
While this is true that posting video/audio/pictures is as easy as posting text, but text is still the default format for blogging. Particularly if you are working on a blog for your startup, it should necessarily have text posts as corporate blog are generally more formal.
However, posting only text is also not a good idea in this Web 2.0 and socially connected world. Currently most popular blogs follow this strategy of "mixed content" where they post two text based posts, then post a video, then some podcast and so on..
The real target is to get blog visitor loyalty, you would have to see what your blog visitors like - text, video, images or audio - and once you know that, you can always change the frequency of posts of either format.
As Ali said, start with text. If you don't, how will people find you on Google? Text is a must.
Other formats may complement your blog posts, or you even may wish to have them in video and audio as well.
It might be subjective, but I would never follow a blog that has mostly videos or podcasts. When posts occasionally contain videos, I watch them for a few seconds but usually I get bored in no time - or I just figure I should be doing something else. I never listen to podcasts.
In short: personally, I prefer text, because even if I'm not very interested in the topic, I can always visually "scan" the text for interesting items. With audio or video that becomes much more difficult. In other words, text is the most flexible format when it comes to information extraction.