Back links are essentially a vote that shows Google how popular or relevant your site is, a directed (voted) form the linking site.
If you have 1000 back links from a site that's not related in any way to your site, will be of no value to you.
Gain quality back links that give benefit to site, are links gained from other niche related and high PR sites.
The best way to do this is create great content about your products an services that people want to read and share. Engage in social networks, forums & guest blogging (to name a few)
The more quality "votes" you earn from relevant, high PR sites and social network engagement, the better you site will rank.
Definitely quality over quantity, 1 relevant high PR back link is 100 times more powerful than 1000 irrelevant low PR back links.