Field conditions are very individual. Plowing over here is very likely very different than plowing in the UAE and fuel consumption is likely to vary just as much. Even mowing (our biggest fuel consumer) varies from year to year depending on several factors - rain being one of the biggest. Overall, for the jobs I've done this year, the Massey has used less fuel than the JD while cutting thicker, heavier grasses (coastal bermuda). So, the MF 5609 performs better than the JD 5425 on my farm in my conditions while being far more comfortable, having more options, and is easier to maintain.
Whether that holds true for the MF 6600 series vs the JD 6R series, I don't know. The MF 5600 series really does not have a competitor in its horsepower/size range. Once you step up from the utility range to the row crop range, it is a whole different story. To really find out which tractor best suits your needs, you need to demo them on your farm.
Glancing through some the Nebraska Tractor Tests data, the MF 6600's appear to more fuel efficient than the JD 6200's when dealing with PTO work while the JD takes the lead when it comes to drawbar performance.