First I used OpenX for over 3 years to serve Ads on all my webprojects,
but after the Google caffeine update when speed came into play I worked a lot on
my forums tuning them with pagespeed and yslow as best as I could.
Webmaster Tools showed a very high page loading time for my major forum.
After that I decided to get rid of OpenX and put the AdSense Codes directly into my Website.
This decreased the page loading speed quite a bit.
Direct sales of my inventory is done by my direct marketer which uses Google's DART for Publishers.
I had a complex structure set up in openX using a waterfall structure to serve my Ads.
I used the javascript implementation method to serve Ads because others would not work on my forums
or I was to lacy to work out a different solution.
Just recently I migrated to DFP SB (see at the top right there is a language switch by the way
) because
I needed to run split tests again.
Took me about 2 days to comprehend the architecture of DFP and how it works but after that it worked fine.
Can't say that I notice any loading speed changes on my websites but webmaster tools will tell in about a month.