Are you talking about posts that are about SEO? Or would you like to know which is better SEO practice for all kinds of topics?
It depends on your writing skills and on how interested the audience you're targeting is. Nobody wants to read War and Peace, but at the same time, a very short post also offers very little value most of the time.
I'd say keep it to one page, give or take (maybe between 1,000 and 2,000 words) as a baseline, and you can vary that based on how good your stuff is, the feedback you get, and generally what you're trying to accomplish.
Basically as long as you can capture and hold a readers attention, and it doesn't feel like a chore to read the article/page, then you've done your job.
As far as the SEO merits of more content vs. less, I'd say the above still applies for the most part - compelling and valuable content is valuable regardless of the exact word count. As long as the page accomplishes what it needs to and is of high quality, you should be fine. But I wouldn't say you're likely to rank with 100 words on an article page.