Direct - DC and BlueLithium brings nothing more to the plate for you if you are going to spend $2-300k/month. You will be placed on yield manager and start to rock and roll. If you have an established relationship with DC or lithium then price them against each other. But you will most likely have a better shot at getting better traffic rather than remnant if you go direct.
BL was bought about two years ago by Yahoo. Yahoo took the technologly and wrapped it into what is now the 'Yahoo Performance Network." So the brand BL is dead hence the issues above but the same thing can be achieved by going directly through Yahoo.
As far as pricing goes direct is always the best price. Everyone including ad networks pay the same price for our inventory so when you buy via a 3rd party you are paying a margin.