Nofollow links do not pass link juice - Google may still crawl them for informational purposes, but they won't count toward your overall domain profile quality. I would only pursue sponsored posts/editorial links if you're confident that the blog's audience is a good match for you - i.e. treat it like an ad, not like link building.
I would be extremely cautious about buying sponsored links. If the person doesn't disclose that they've been compensated for a blog post, they could be in violation of FTC guidelines. A reputable sponsored post SHOULD nofollow their links, otherwise you would be in violation of Google's paid links policy: http://support.google.com/webmasters/bin/answer.py?hl=en&answer=66736