I chose the 5.7 because in 2015 it didn't have MDS and I didn't want extra parts that may fail. Also, they recommend premium fuel for the 6.4 when towing, didn't want that cost either! I have 326K miles on my truck now with only the typical exhaust manifold studs breaking, they eventually had to replace the manifold. Only other issues were the water pump and of course the transmission had to be replaced at 280K. 90% of the mileage was towing an 18' open, 24' enclosed, or 32' LQ trailer and I will say that the 5.7 is adequate, not great for towing the larger trailers. I am glad I didn't buy the 6.4 with the amount of fuel I have bought over the last 6 years...