I think intensity would be more efficient for adding growth, but is more likely to cause algae.
If you don't have any algae right now, increasing the light intensity is a good idea I suppose if you want to stimulate growth. However, if you have some algae as it is (or even if you don't) then increasing light intensity may cause more algae to grow and outcompete plants, which is the opposite of your goal.
If you can lower your light an inch or two, you should start with that as long as algae isn't a problem already.