I have a fairly simple theory on linkage.
*Incoming and outgoing linkage is more important than exchanged links. The reason for this belief is that usually incoming and outgoing linkage is relative to content.
*Exchanged links are an agreement between web sites to make a link to one another. Although recent exchanges are based on relavence, relavence is not to content but to industry.
*Even bad linkage, can qualify as good linkage. But, best linkage is linkage being used to bring visitors to your site.
*I do not care how high your linkage improves your ranking on Google or any other search engine. If linkage isn't providing visitors and searchers aren't searching for your keywords, number one ranking doesn't mean a damn thing.
*SEO means Search Engine Optimization. It is intended to make your web pages Search Engine FRIENDLY. This does not "promote" your web site or product. It provides person with better optimization ability to rank higher on search engines results than others. (And, if you think about it, it's allowing search engines to dictate design and content of your web site.)
Even if search engines never spyder another web site, linkage will continue to promote your web site. With this premis in mind, what type of linkage should provide you best promotional result? If you haven't yet decided on content as answer, I'll give you a few more minutes . . .