I bought a 2011 ecoboost about 3 months ago. I test drove both the 5.0 and ecoboost quite a bit. The power of the ecoboost is what really made up my decision. Has about 11 000km on it right now and absolutely love it. Smooth, quiet ride with more than enough power when I need it.
I work out at the rigs so I do a lot of highway driving + lease roads. My mileage since I purchased the truck (11000km) is about 14.0 L/100KM.
My mileage for highway driving with cruise control is somewhere around 12.5L/100km.
Try them both out and see which you like better, but IMHO +1 the eco.