If you have 50k unique visitors per day then which CPM would guys recommend?
Go for 'Exponential Ad Network' formerly the Tribal fusion. Its the highest paying CPM network.
Apart from Exponential, Adversal is also very good option for you.
If you already have 50k unique visitors than why do you wanna involve a third party ad agency. Go for direct selling ads. It will exclude your commission to the ad agencies and hence your income will increase accordingly.
It will be a great opportunity to have other related ads rented in your site page for you to have income and improve better to increase more visitors.