Best way is to test them all by yourself
We made a tool for this, just send to each 50.000 views with the same conditions and then analyse and compare them.
How many views did you serve > how many views are they showing in there stats > what they pay for it. (you just have to place your earnings and system generate a complete overview)
Then click on highest Ecpm and this is the better one to use for that moment. Best is to send 5% of your total traffic to different brokers and check every week your highest Ecpm.
Donīt forget to check the price of the payout and minimum payout
some charge % or fix price to get your money. Lots of different between $ en ?
Here you can find the free tool
The next step of performance network
Contact me on Skype for a demo envivomedia