I came across this blog post about using two ad networks, one to pick up after the other.
It looks like he uses iAd primarily, and then a smaller one to get the fill rate the other one misses. Does anyone else do something similar? Or use different ad networks for different apps?
I would say that you should choose your networks according to your geo locations in terms of the traffic that is usually coming in. If one app is famous is Location X, then get the network that gets you the best fill rate on that Location - however it is difficult to find a network that will get you a good fill rate in all locations. So in this situation, it would be wise to have multiple networks to rely on.
If your traffic is coming in from a location of locations that a network can easily and consistently accomodate, then you should certainly go with that network and keep with them with close monitoring.
Good luck. 
Bill
Having multiple ad networks is almost always the right call both for building in a contingency if one goes sideways as well as to test new options. Even if you’re seeing an increase in rates month over month from your primary network there may be someone else with better inventory, more relevant ads who can outperform and you should be testing that on an 80/20 at minimum… In most cases it’s even better to divide into 30/30/30/10 or whatever makes sense from a profit perspective.
Yeah
You are under no obligation to stay with just one network…if a network gives you good results and does so regularly and consistently, then obviously there is no reason to disturb such a setting…but if you think you can do better…go right ahead…all you have to make sure is that your Fill Rate is high up and of course the CTR (Click Through Rate)…it is your site/app, and it is you who is making the money…so make sure you monetize your real estate properly…
I also use multiple ad network on some of my sites. Having the mind set of if your visitor is going to view multiple pages on your site, why not show them multiple ads. Then split test them and see which one generates the better results. This also help if your ad network will only produce so many ads per unique visitor.
I think you hit the nail with the last line. The most profitable ad is going to be on the frontpage and to evaluate which one is doing well in that setting is not going to give you accurate results. Unless you switch their positions every now and then and what not. Even in that setting you would have to closely monitor the number of visitors on your site to be fair. All in all, it would take a lot of time. I would just use multiple networks based on my geo locations and that is about it. I would monitor the performance of the networks and if one falls short, I’ll switch since there are so many of them. Also, I would also want to be sure that I am using ads that are relevant to the content on my page.
Let me know what you think…
Cheers
Bill
DISCLOSURE - I work at Tapit Advertising
Yeah, I started shopping around 1-2 months before I made my post and it’s been pretty fun. I feel like a lot of people are a little late (me too 
) on getting a couple networks. Also made me realize how much adMob is resting on its laurels! A lot of the new networks are breathing more exciting life into the mobile ad space for sure.
All I hear about the big names in Ad networks is that their Support sucks…if I as a consumer would want to join someone, I’d rather join someone whom I can speak to over the phone or get a quick and helpful reply on my emails…and Support needs to be there with all the competition around…
I use 2 ad-networks on my website to fill my remnant inventory. One ad network buys only the first impressions on CPM and then I sell the rest to Adorika Media Group they bring me great results for this traffic.
[FONT=Verdana]As this thread is almost a year old, and the OP has since left, I see no point in resurrecting it.
Thread closed.[/FONT]