Metapilot - 10:07 am on Oct 22, 2009 (gmt 0)
I've owned both for years and they each have their pros and cons. Optilink is better for breaking down and examining the individual words that make up the anchor text of a site's backlinks, while the raw data provided by SEO Spyglass is better for sorting a wider range of backlink information. Neither is going to give much help in understanding the VALUE of each backlink--you'll have to know how to do that yourself but SEO spyglass does attempt to do that for you. Of the two, SEO Spyglass has a more user friendly interface.