Which among the two contributes most of the lift, the upper or lower surface of the airfoil?
In subsonic flight, the majority of the lift is generated by the lower pressure (compared to ambient) at the upper surface of the airfoil, which produces a net suction. A portion of the lift is also provided by the lower surface that has higher pressure, but is much smaller in comparison.
The graph below shows experimentally derived data on a symmetric airfoil, which breaks down the pressure distribution between upper and lower surfaces. The vertical axis of the graphs shows difference between local static pressure and free-stream static pressure divided by dynamic pressure, which is also called pressure coefficient. Note that a negative number means lower pressure compared to free-stream static pressure, and is suction; a positive number means higher pressure, and is pushing.
As you can see, in the 9deg AOA case, the upper surface suction dwarfs the lower surface push force by observing that the area under the curve is much larger for the former.

Image ref: http://web.mit.edu/13.021/13021_2003/Lifting%20surfaces/lectureC.htm
The next two plots show the stall and post-stall. This airfoil stalls at leading edge, so the entire suction peak is removed once the flow is stalled.