Both…and more.  Social media, press releases, good articles, content on your website, backlinks.  All in moderation and without taking shortcuts.  Google seems to catch on to shortcuts pretty fast, so just when you think you have found a great thing, millions start doing it and Google clamps down on it.  I haven't really changed up my strategy since my first time around.  Good content sprinkled around the web will always benefit.

A few years back it was article marketing.  Then tons of people started buying crappy articles in huge quantities and dumping them on directories and they were de-valued. Ezinearticles once ranked really well.  Not anymore.  Goarticles still ranks fairly well.  

My article directories are starting to get some traffic and they've only been online for a month.  People are finding articles with long-tail keywords, so clearly article marketing still works, even though many say that it doesn't.