Depending on what you are doing - you know your audience best - from a marketing point of view you are almost always better off writing long articles. Articles longer than 2000 words are more likely to rank on Google and be seen. This could be because they are more impressive, more thorough and as a result more likely to be shared - longer articles get shared over social media far more often.

If you are going short you would be better vlogging or creating graphics because people engage better with shorter videos and like images. Short videos are more likely to rank on youtube because people watch the whole thing - proportion of video watched is a strong ranking factor. The most important thing I would say though is don't write a post which is longer then what you are able to think of content for - don't put in artificial fillers - this sounds obvious but a lot of people do it. It is a good way of losing your audience.