I would suggest one photoperiod plant, topped and SCROGged as giving the best yield, as this way you can control the veg period and switch to flowering only once the space is completely filled.
Forget autos if yield is your goal, they will flower as soon as they are old enough and may not come close to filling your tent before they start flowering.
3 plants will fill the space quicker, but you get a lot of smaller buds growing beneath the canopy.
I have tried both ways and the SCROG method wins hands down. It may take a bit longer to fill the space, but there is much less work involved with only one large pot and having only one plant to worry about keeping hydrated and well fed. Having an even canopy via the SCROG net also ensures you get mostly large flowers all growing from the same plane, maturing at the same time and with some well considered "lollipopping", a minimal amount of small shitty buds.
If you only have one light, setting your SCROG net in either a slight vee shape or bowl shape, will allow the outer branches at the edge of the tent to be closer to the light and basically receive the same amount of lumens as the flowers growing directly beneath the light, as light intensity lessens over distance. With 3 plants under one light, this would mean each of the three will be growing away from the centre of the tent and into areas of diminished light intensity.
Hope this helps,........
Organoman.