The fact is, nobody can control who links to your site. If you are posting with links to your site, related sites/blogs are best.
It will still count, but it is debateble how powerful the backlink will be. Some argue that backlinks from sites in an unrelated niche are useless, but I had a link from a PR8 site that wans't related to my in any way and it really helped by ranking.
The best links are those from related/authority sites. From my experience you are better off building 1 high quality link rather than 100 low/no quality links.