Me and my friend are doing a project and in our result we shall provide a plot, and on our axes we are going to write out the units. My friend wrote "xx MPa", claiming it was standard in reports to write Pascal with the prefix Mega. Well, I claim that there is no such thing, you simply write it with the SI-unit, hence Pa. What would you say?
Both are correct. It is a matter of personal preference which you decide to use. It makes the graph easier to understand if axes are labelled in small numbers; it also makes the graph less cluttered. So either you would label the x axis "Pressure in units of 10^6 Pa" or "Pressure in MPa". Labelling the x axis as "Pressure in Pa" and using marker values 1x10^6, 2x10^6, 3x10^6, etc is ugly and looks unprofessional.
So it all comes down to the same thing. Not worth spoiling a friendship to argue about!