In terms of SEO, it is unlikely to make a huge difference. Putting the category in there might give you a tiny boost by having the extra word in the URL. Assuming you'll have an index page at sitename/articles/category/, this probably will help your search rankings, because it provides spiders with an easier way to navigate your site, and helps to chunk the information into related sections so they can understand how the site fits together.
In terms of usability, there are pros and cons. On the one hand, the extra level of navigation may help people, because again it gives them an easy route to find related articles. On the other hand, having the longer URL means more chance of mistakes when people type it in.
Also think about it from the point of view of your site maintenance. Will it be easier for you to keep a handle on if the articles are subdivided by category or all in the same place?
The answer will at least partly depend on how big you intend the site to get. If you're thinking of having maybe a dozen articles, that subdivision almost certainly won't be necessary. If you're looking at having a couple of hundred, it will very likely be helpful.