Both are important, but everything starts with the content first, then builds from there. It is no use building good back links from web 2.0 sites to really poor content. A while ago marketers used to say how they could get tons of traffic to a single page website just by backlinking. I dare say some can still do this. However, there is not much point driving the most targeted, cash rich traffic to a site that has utter drivel on it.
So get the content side of the equation working first, then start building some good quality back links to it.