3 1ft plants generally, i mean if the 3 foot plant has 10 large top colas then of course it will be better but if you have 3 ft of growth straight up you will have bud at the top and not the bottom, wheras the 1ft plant have bud over most of the 3 ft covered. Im not sure if it would work in this instance, but if you grow say 10 smaller plants and 5 bigger plants in the same area you will get more off the 10 plants than the 5