The best unit to express the weight of a Boeing 747 is tonne.
Work Step by Step
We would like to use a unit which gives us a comfortable number to work with, that is not too big and that is not too small such as 0.00001. Clearly the units of milligram and gram would be too small for expressing the weight of a Boeing 747 because the number of milligrams or grams would be very big numbers. A Boeing 747 is so heavy that even units of kilograms are too small as the number of kilograms would also be a very big number. The best unit to express the weight of a Boeing 747 is tonne, because then we would be able to express the weight with a number that is not excessively large.