which is it called? I honestly do not have a clue myself. 1. "I went to the classified site and looked through the classifieds" 2. "I went to the classifieds and looked through the classified section" this is messed up.....
3. "I went to the classifieds and looked through the classifieds section" Classified isn't classifieds. A website with tons of small ads (like Craigslist) is called a Classifieds website with classifieds.
i'm used (i could be wrong) to using "classifieds" or "classified ads" however keyword analysis is really the important factor.... whatever more people use...
Try Google's Translator and see what the translation is: http://translate.google.com/ To me it shows that "Classified" means like "We classified this laser as a class 3 laser", while "classifieds" means advertisements (like Craigslist)
Classifieds sites and posting your ads on classified sites is good for seo too and you can get benefit in terms of product's selling.