There is an updated version of this post here – Google Ad Manager vs OpenX vs Trafficspaces
I came across this interesting comparison of OpenX and Google Ad Manager on Mahalo
Here is a summary:
1) OpenX is an independent, neutral provider – a point which Bernard Lunn expanded on here in a March 08 post entitled Manifesto to Avoid a Google Media Monoculture.
Tim Cadogan claimed in the call that OpenX complements what Google does – by which he meant that it can arbitrate between ad networks, including Adsense. Although Tim Cadogan didn't say it directly, the inference is that Google's Ad Manager can't do this arbitration as fairly.
In his March post Bernard made clear what the dangers of using Ad Manager are:
It is the integration [of Ad Manager] with Adsense that is a worry. [...] Take the link to Publisher tools and you get to an Adsense page with all the tools available for Publishers. Yes, all these free tools are designed to sell more AdSense. Letting Ad Manager and other Google tools automatically make these decisions on behalf of AdSense while you fly blind is not smart.
Simply put, what Bernard Lunn is insinuating (rightly or wrongly) is that Google can use information on Ad Manager to pay you less revenue from Adsense. This is particularly worrying problem for publishers who are struggling in a recessionary environment.
2) The second difference between OpenX and Ad Manager, according to Tim Cadogan, is that
OpenX is open source and "infinitiely customizable". Examples of companies using OpenX Ad Server are FM Publishing (another disclosure: they are our ad network), AOL's Userplane (for Enterprise), Dragon Media Online (Enterprise), and AneXusIT (Video).
Good point. The future is definitely in giving publishers more control. OpenX does it well butTrafficspaces does it one better by making it super easy to make those customisations. OpenX can be a bit too technical sometimes.
3) The third difference is that OpenX is "very very feature rich" compared to other ad servers – and not just Google's, noted Cadogan. OpenX does have a lot of features, many of which Trafficspaces matches very well and even exceeds.
Google Ad Manager still has a long way to go but I guess they have conflicts in how feature-rich they can make their product without cannibalising their premium Doubleclick products.
In summary, the market for self-service ad management systems is getting very interesting. Each product has its strengths and weaknesses and will appeal to different publishers depending on their needs.
One size definitely doesn't fit all.