There was a couple of rather lengthy threads a while back about wing lift (and prop lift since props are just wings that are spun up rather than pulled through the air).

Try a search on "wing lift" within the Aerodynamics forum only and you should find a bunch of old threads that deal with this. The juicy ones are those with reply numbers over 40.

Basically for a wing to produce lift it must fly at a positive angle of attack, have camber or have a little bit of both. Once the wing is developing lift you will see a higher than ambient pressure on the lower surface and a lower than ambient pressure on the upper surface. Linked to this pressure you will see the air undergo a change of direction as the wing passes by that produces a downward motion of the air. If you analyse all this you will find that the upper to lower pressure difference over the wing accounts for the lift being produced. Similarly if you study the air being deflected downwards and do a mass to velocity comparison you will find that the energy added to that air to move it down also accounts for the lift upwards. Which of these is the actual lift is like asking which came first, the chicken or the egg. And that was the basis for quite a bit of colorful posting in past threads. In the end the two effects are simultanious and linked.

So you see, one surface does not supply more or less than the other. It's the pressure difference between them added together. Alternately you can show them that the air is defected downwards so the wing is just acting in a classic Newtonian action and reaction mode. But as said, both effects occur together and change in step with changes in angle of attack, speed or camber (flaps). They are in lockstep and one effect is totally dependent on the other. In fact I think it's fair to say that they are different aspects of the same thing or that they are actually both part of one integrated effect that "we" just find it easier to look at as separate effects.

....at least that's my story and I'm sticking to it...