The real deal on container size

Ok guys, this is my first post, and I would like some opinions.

To avoid all chance of becoming rootbound, and to maximize yield, what size of a container should I grow in?? I have successfully grown in 5 gallon buckets, but noticed growth being stunted usually by middle may. And I have herd people saying that more like 30 gallon rubbermaid container is optimal. Instead of many smaller plants, I would just like one or two as big as they can get. So what's the real deal???

oh yeah, the two girls im gonna keep are already about 24 inches tall. this is why im concerned on what size container to transplant them into. They are in 5 gallon now, and when i lift them up can see plenty roots. I can tell they will need to come out in a week or 2 at most. I have some approx 10 gallon containers I can use, or should i get something bigger?