Are you referring to the V6 in the newer JKs? If you're referring to the Pentastar engine in the 2011+ JKs, it is worlds better than the 3.8 Minivan engine found in the 07-10 JKs. That Pentastar is undoubtedly better and more efficient than the I6 by far.
However, I will say that the I6 is pretty much a tractor engine, and what it lacks in mpg it makes up for in longevity and strength.