Ezine Articles is the number one article directory because the rich article directories just get richer. Infobarrel is gradually catching up due to it's profit sharing. The main feature that Ezine Articles has over Infobarrel is the syndicated content(I do like some elements of the Ezine Articles editor more than Infobarrel but Infobarrel makes it easier to insert links).
When we studied Google ranking factors using advanced search we found that the hardest criteria to meet was to meet the title. Google was flexible on keywords in domain, post, and links but not on title. It wouldn't even count the title of the post it had to be the title of the site.
That's where the syndicated content of ezine articles comes into play. No matter how much Google loves Ezine Articles the title of the site will always be Ezine Articles. Whereas if your post gets syndicated it could be syndicated on a site that has your keywords as a title. Usually, the sites that syndicate the content don't have search engine friendly titles like my content has been syndicated on movie matic(Movie is a good keyword) and people's health portal(people and health could be good keywords but not for most health terms).
By Ezine Articles syndicated content your content may be syndicated on an article site that has a better title for your keyword. Now how good this title is depends on how broad your keywords are(like Movies and Health). Otherwise, you might as well post on infobarrel(and then use ezine articles to link to infobarrel as tier three or below of the link pyramid). I think it would be easier to blast backlinks to a site with a good title that corresponds to your keywords then it would be to ezine articles despite their domain authority(unless your site keywords are ezine and articles; but hey maybe your site keywords are info and barrels).
There's also the advantage that you can self syndicate the ezine article to other article sites but me personally I would rather just use infobarrel.