What are the best ad networks for advertisers in the United States?

This is entirely dependent upon the platform you require (are we talking mobile or web here - you've posted in both?) and what formats you are wanting to run. All mobile networks (my specialty) will essentially fall into one of your 3 definitions pretty much. So it also depends on the requirements of the campaign? Drive users to sign up/download, is it a pure branding campaign, convert users to spend, types of users wanted etc

What type of advertising are you interested in? There are video ad networks (like Tremor Media), online radio ad networks (like TargetSpot), television ad networks (like REVShare) and of course online ad networks. (Caveat: I've worked for the three mentioned.) Advertising Age produces a special report on ad networks each year, which might be a good starting point for discovery. Just keep in mind that the individual profiles are written by the ad networks. http://adage.com/adnetworkexchangeguide/

Here's a list of the larger ones: - AOL - Conversant - Specific Media - Matomy - CPXi - YBrant Digital - Adconion - Adtegrity You can get a more comprehensive list at http://thalamus.co We'll have network reach by channel data in the next few months

This depends upon number of parameters and as per the advertiser or vertical, there are number of ad networks in the market now who are good at some part and bad at some part. the general guidelines to follow before choosing an ad network can be referred here: http://www.knowonlineadvertising.com/how-to-choose-an-ad-network/ Top Ad Networks by ComScore: http://www.knowonlineadvertising.com/20-largest-ad-networks-2013/

Well, I have come across with a site called xpedient media, Which  provides complete advertising solutions. Basically it is an online  advertising agency. Xpedient Media offer Content Marketing and Blogger Outreach services on a wide range of Blogs and Publications in the most sought after Business verticals like Health and Fitness, Travel, Beauty, Fashion, Home, Lifestyle, Food, Technology, Business, Entertainment,Parenting, Automotive, Sports, Games and so on. I have taken their services for my business. I got  good ROI out of it. for clear understanding visit to http://www.xpedientmedia.com

It is hard to pinpoint one ad network to answer your question. The quality of content and visitors depend on how good it will fit with the content you are offering. The better the fit, the higher your CTR's will be and the more revenue you will make. Every network will be different and some will fit better to you than others.  The best thing to do is to A/B test different networks and to see which network serves your website(s) best (read: will generate most revenue). One of the networks you should consider ishttps://www.exoclick.com/?login=home. They won several prizes over the last year, including to be the most disruptive tech start-up in the advertising space and grew just in a couple of years to the top 5 ad networks in the world! Focus on revenue and let the numbers decide!