I usually like to write articles in the 500 - 700 range. 300 words is not enough to clearly talk about a topic.
There's also a question on return on investment. The is a lot easier getting a roi on 400-500 word articles than one thousand word articles. Not to say that you shouldn't mix it up a bit and have some longer articles.
The answer isn't black and white. The short copy may be better for SEO and ROI for publishers. But the long copy is more favorable in selling products in selling products and services.
I believe that for publishing 350 words are a good target. The issue is to get a return on the investment which will be harder for longer copy.
My opinion, and this is the standard that I have set for myself, 400 - 600 words is good. A lot of my articles include images and sometimes a video.
Writing the article, finding the images on my computer, resizing the images, watermarking the images, embedding the video, spell check, proof reading,,,,, when an article gets in the 1,000 word range, I'am usually looking at at least 1 - 2 hours to write that article.
Its easier to break that 1,000 word article into 2 - 500 word articles, give them different titles, different tags, interlink them, and leave a slightly larger footprint in the search engines.