Actually, I think you can do all of that with both. There is certainly demographic targeting, and you can serve your own ads (ones you sold) and ads from their network if you want. There are a lot of options in OpenX and AdManager.
Go to http://adroll.com sign up. Configure your account and it will generate code you can put in text boxes on your site. Then the companies you spoke of can advertise in those boxes. It helps to use the tab manager and add a direct link off your home page to the page built for your website by adroll. Just name it advertise and point it to that page and make it one of the main tabs and tell it to open in a new page. You can see this is action on my site http://hhoinfo.ning.com
Hello friend, I can announce I do for my own ads use a text box and use this website (http://www.htmlbasix.com/banner.shtml) is a banner rotator, this site will help you if you want to use images you configure the size and decide if you want this to change every five seconds or when they change the ad page change too, I hope I've helped.
Been using OpenX, but in my opinion, it is a very difficult site to mange. Also, They are now beginning to server unauthorized 3rd party ads to my site. There's absolutely no customer service. No one to talk to email with. I'm moving off of OpenX.