It's a little like asking, "How long should a novel be?" or "How long should a newspaper article be?" The better question is, How much do you have to say?
Proclaiming that "short blog posts work better" or "long form content works better" is silly, because content doesn’t work that way.
Compare "The Old Man and the Sea," which many consider Hemingway's finest work, with the J.K. Rowling classic, "Harry Potter and the Order of the Phoenix," loved by generations of fantasy readers. Here's how they stack up in length:
Obviously, what matters is not content length, but content quality.
Web usability expert Jakob Nielsen wrote a 1,700-word article answering the question of ideal content length, ultimately concluding that a "mixed diet" of content is best, with some short posts for easy readability, and some longer posts giving more in-depth information.
It took him 1,700 words to say it, but we just summarized it in 170. Enough said.
Next: The importance of images!