Well i think .edu & .gov domains can give us authority backlinks yet some forums are also good in this respect.
I always strive to obtain backlinks from websites in the same market as my own. I feel these back links not only give a good ranking with google but also allow for a better source of concentrated traffic to your site.
It depends, I only build links through forum posting so those links are most beneficial for me. I wouldn't look into to much, and just focus on building links, and not where you build the links. Obviously sites in a similar niche are better to build your links, because they will help you rank.
Back link from Forum posting, Blog commenting, Link exchange is more effective for a good page rank. Link from facebook, linkedin, twitter is effective to get a good traffic. Thanks Farabi
Recent penguin update has lot of changes in algorithms. You need to have quality links from authority domain names. You need to have backlinks to inner pages too. Best method to get such links is article submissions to quality directories and forum postings. It is also advised to have your keyword as anchor text.
Let's not forget to be careful of reciprocal links as they may blacklist your website if the owning website is involved in Black Hat SEO.