Pretty simple question, with hopefully a simple answer. Also, how many article submission sites per article? What about duplicate content? When is duplicate content duplicate content in google's eyes?
There are only a few top article directories, the rest I would categorize as pretty much the same so I wouldn't waste time on analyzing them. Just submit to the top ones (there are lots of top lists which are all pretty much the same, just search and ye will find). As for duplicate content. Duplicate content is duplicate when 1 or more of the same content is posted. You should rewrite your articles before submitting a unique version to each site. Google "article spinner" there are a few tools around that can help you with this process and it's down to how well you use them as to the quality of the articles that the tools produce. HTH