We manage SEM for around 20 clients who use both Adwords and Serps.
Recently first page results for their keywords average:
Adwords: two duplicates, two PPC affiliates and two/three spam.
SERPS: 1 or 2 PPC affiliates
The conclusion? Serps look a lot cleaner and more relevant.
I would only wish Google/OV/ES etc would deal with these PPC Search Engine affiliates. They send users round and round in circles between the PPC engines, offer users no content and yet rack up cost for the advertisers.
Never heard of Serps - I'm probably too poor for it though. I've paid nearly $30, without a single conversion. Most of my clicks on the content network (which outstrip the search by about 25:1) are from AdSense farms or crackz/warez sites. Does this Serps somehow filter that garbage out?