What type of link back is the most valuable? Recipricol? Directory? Blog Post? Other? In terms of SEO
Reciprocal - not so much. Even if it is a related type site. Directories haven't done much for me yet. Blog postings - Good! One-way link from a related site - Great! Three-way links in a related network - Awesome!
Sponsoredreviews will give you one-way links to your site, so this is good. However, if Google decides to go after the advertisers who buy links, you may end up paying more to ask all those bloggers to rel-no-follow your links.
to answer your question, the most valuable link you can get will come from a website ranking in the top 10 for your targeted keyword, however this is not always possible, so doing a mix reciprocals, directories and niche directories, relevant blog posts.. will help your website achieve better rankings. good luck.
As ssandecki and angilina said, one way links are the best. However, I am going to expand upon that. You want links from relevant Web pages (note I said PAGES, not sites) that have a high PR (PR 4 or higher) that rank well in the search engines (top 1,000 results for the key phrases you're targeting) and contain the keywords you're hoping to rank well for in the anchor text.
Depends on the relevancy of the page that you are obtaining it from, the PR of that page, the nature and number of outgoing links on that site and the anchor text used.