Picking up again on the necessity of diverse backlinks, all domains that we submit to are public websites.  We do not participate in any posting networks, link farms, nor do we submit to any “exclusive” domains that (more often than not) the SEO company just owns themselves.  We scrub website data to find specific sites that have posting or link building opportunities (blog comments, guest posting, etc.) and submit to those.  That way you have backlinks from similarly related websites, industry leaders, and some miscellaneous websites for a nice balanced link portfolio.