Velocity vs Pressure contour
 

Which would be better in a report on aerodynamics, velocity contours or pressure contour?

Which ever explains the message you are trying to convey better. Only you can answer that question.

Well, I want to show the flow around the wing.

They are both different aspects of the flow around the wing.

Or combination as follows:

1) Plot pressure contours and black vectors
2) Plot vectors coloured by pressure