I think you have to experiment with both options to determine which one does it for you. Your attack angle, your clubhead speed, etc. can influence the results. I have seen the stiffer shaft more loft work for some, and the more flexible shaft lesser loft work for others. For me personally, although my speed indicates I should play an X, I play a lighter weight (56 gram) S flex with an 8 degree driver. That gives me the launch window and spin that works for me in my current state. I have tried more loft with stiffer shafts and if the cg of the head is in a position that helps keep the ball down, I can generally get to the launch angle I like, but the spin is still higher. So, I have tended to stick with the slightly more flexible, lighter shaft and the lesser loft. Again, I think you will need to experiment with both to see what works best for you.