For MPG if you drive both engines conservatively you will get about the same mileage.
The ecoboost makes much more torque, so if you stomp on it for both engines the Eco will burn more fuel. That is because it is making more power.
There have been very few turbo issues, and all the problems for the engine have been figured out at this point.
Both engines had their troubles, the Eco was condensation shudder and spark plug gaps. The 5.0l it was oblong cylinders which needs a whole engine block replacement.
Majority of the people on this forum love their ecos. Myself included. When you tune them they become a powerhouse.