This is one of my favorite SEO topics. Link value is determined by 2 things (with a bunch of other small things as well, but two major things), traffic and the authority of the site directing traffic to your site.
So, think of the site's DA as its numeric reputation. Obviously the higher the DA, the more reputable and trustworthy the source, in most cases. I have come across pay day loan sites with DA of 70+, but the general atmosphere of the site was extremely spammy. The value of a link with a DA of 80 is far better than having 10 links to sites with DA of 8. The same number, but diluted value and obviously less reputable.
The link juice is generally passed through traffic, which is why links with images and videos that encourage a click are more valuable than just text at the bottom of a page buried in content. If you have a video on a page, above the fold, from Vimeo or YouTube, that would be considered an amazing link, because it will have a high CTR, drive traffic and is from an extremely reputable source. Link building is not about the quantity as much as it is the quality of the link. This is why content linking is important. Granted, that can't be your only form of back linking, it almost insures you will have relevant links to sources that can generate traffic to your site.
You back links are the highways and byways between Google and your Site. They show the engines that you hang out in good neighborhoods and you aren't trying to manipulate your site's value by creating "short cuts" through dark alleys with less reputable company.
Hope that helps.