Answer:
The main reason for the variation in format has to do with the country you are in. January 26, 2017 is the preferred format in America, while 26 January 2017 is the European form.
Step-by-step explanation:
The main reason why it would be better to use 26 January 2017 would be because this format is used in a larger number of countries. However, the choice to use one format or another would depend on where you are or who you are writing to. If the recipient of the document is American, they might prefer the first format. If, in contrast, the recipient is European, then they would prefer the second one.
Other than that, the use of one format or another is simply a cultural convention.