Approval sites are always better due to acceptance of quality content. Non approvals are mostly spammed not good for SEO.
Non Approval sites are an absolute waste of your time and energy. Approval sites are slightly less wasteful, but in reality unless your content is particularly viral, I would spend little to no time on article submission sites if you're doing it for the purpose of obtaining a (extremely weak) backlink. WebDev
Its true that high PR article directories approve only quality content, it also depends upon editorial team following there own guidelines and enforcing them.
There are hundreds of article directories that will reject your article's. It's just a matter of the owner or editorial team following there own guidelines and enforcing them. I don't see the point of your question.
Additional Approval sites have 2 types: 1) Do-follow 2) No-follow Only get links from Do-follow websites. Do-follow sites are better for your search engine ranking. You can use Google extensions to check Do-follow and no-follow sites link.
No article directories are good these days. All of my sites that I built links from article directories have received unnatural link warnings. They are worthless and dangerous means of building links these days. Guess which website was the number one website that Google showed me as unnatural on my links? Ezinearticles.com. Theres very few better article direcotires than that one, and if I received a warning from those links than all directories are a target.
In my opinion there are no different approval and non-approval article sites. There are only sites that approve your article as per their rules and guidelines. If your article doesn't meet their set criteria then they may not approve your article and if it is as per their conditions then they may approve your article. And most important articles are written to share information with people, to make them aware of the things you know, so don't always try to create back links for your site.
Well, off course approval article sites are more good then no approval. But the thing that you have to keep in mine that while submitting article on fast approval article sites, page rank and traffic of that article sites.
I suggest you if you have unique article then do not submit it any article submission sites. Submit it in various blog posting sites like wordpress, blogger, etc. It is more beneficial than article submission