When I tired LinkVana it was pretty poor. Mostly low grade PR2, high post rate, sites got de-indexed in Google. I tracked some of these sites for a while and could see they were still posting to these de-indexed sites 6 months later, i.e. 6 months after sites were de-indexed people were still paying to put links on them.
This was some time ago, perhaps things are better, but I would go with BuildMyRank personally, a vastly superiour service to LV, though not as good as it was.
Of course neither of these are really "high quality" networks... but they are the best of the public paid ones widely known... the really good ones are in the hands of large SEO firms.
I saw a great network a while back, must have cost a fortune to build and operate... all PR5+ with original content, only one in three posts had links in them, they looked legit unless you knew what you were looking at.
These were linking out to some really big customers, an international bank was one of them... trying to rank on a specific financial service.