coachm - 5:07 am on Nov 17, 2010 (gmt 0)
I've used both extensively, including local versions of openx on servers, and VPS and their hosted version. Here's the thing. Openx is a company that is under-resourced for what it does. Their program gets worse as they add features, support, even if you try to pay for it is non-existent, and you WILL need it at some point.
Here's a trick. Check out the official support forum and notice how many questions are NEVER answered or resolved. That says a lot. Openx is a disaster, and the issue isn't if you will have problems, but when, for either hosted or using it on your own server.
I'm not a fan of DPF/GAM either, but it does what it says it should do and it's reliable. The interface drives me nuts, but it's always available, unlike openx which decides to not work for hours, days, or for some people weeks.
So, after years of using openx, we scrapped the entire thing. Closed our VPS down, and now rely on GAM.
One note. It's only a suspicion, but it looked to me like serving adsense ads thru openx was affecting earnings negatively. It shouldn't, but it IS possible. In fact, after hundreds of thousands of impressions, we ended up having most of our adsense ads coded on page, and not sent thru server.
I'm not seeing this when serving via GAM.