The most powerful Link Building Method

In terms of rank, I'd say whichever gets you the high PR link. So merely by its nature that's usually guest blogging or homepage links from other blogs. Even if you find a high-PR auto-approve blog post to comment on, there are usually so many other outbound links that it dilutes the juice.

In terms of traffic, I'd say Twitter and Facebook provide the most hits, but you MUST have something of interest to offer, preferably to give away. Forums in your niche can also bring in a good amount.

As you mention there is no just one link building method that works by itself and additionally you should not use only link building in order to get traffic.

Anyway here is a list of what works best both for link building and traffic generation

1) Guest Posting: Writing guest posts on authority blogs on your niche will not only give you quality contextual links but you will get targeted traffic and become recognizable as an expert on your niche.

2) Video Marketing: Videos rank much easier than articles and it is known that sites with videos rank 53 times better than the ones that don't use videos. Most Video Sharing Sites will let you put a link on the description, even though these links are no follow, a link is a link especially from pages with high PR (most video pages have at least 3-4PR on YouTube and less than 10 outbound links) Additionally you can put a link on your channel which is do follow on YouTube (the Page Rank of your channel will be 0 in the start but the more videos you make the higher your PR will go (it could get more than PR5) and with only your link there it will be a huge boost for your site.

3) Blog Commenting: Commenting on high PR and traffic blogs on your niche will certainly give you quality back links and traffic but you should write quality comments that will add value to the post and not just something like "Great Post" "Nice Post" "I love your blog" etc (most blogs recognize that kind of comments as spam so they are not accepted)

I hope that this list will help you!

P.S Never use software or services that promise that you will get 10000! links or more, all these links are worthless and could harm your site, actually just one link from a guest post on an authority blog on your niche worth 1000times more than these 10000links!