I've used AdRotate Free for a couple of years.
I've since tried out various paid competitors such as AdSanity, OIO Publisher and AdPress. All gave me various issues after working hard with them for a couple of weeks. Then I went back to AdRotate and decided to go for the paid version AdRotate Pro.
Overall, I've come to the conclusion that AdRotate Pro is the more stable and more intuitive of all the ad management plugins for WordPress. Any bugs are usually sorted out very quickly by the plugin author.
The only factor that prevented me from giving this plugin the full 5 stars is the fact that there currently is no option to automatically have rel="nofollow" and target="_blank" added to the outputted code. These basic features are essential in my view and I really hope they're added soon. (The plugin author said he'll consider it subject to demand). The "workaround" is to manually add the code into each ad. Not ideal. I docked 2 stars from the rating as I see this as really important. I'd happily give 5 stars if the plugin had these options added to the settings.