Not really a right or wrong. Personally, I think autoflowers are kind of gay, because you can't clone them, and need to start from seed every time. With regular seeds you can get thousands of plants from just a couple seeds, and not have to buy seeds again for years - probably why the seed banks like autoflowers so much.
I thought he meant 6' wide by 3' deep; height would be more relevant.
The other advantage to non-autoflowers is that, if you fuck them up, you can often times let them recover by extending there veg time. With autos, the timer starts the day you put your seed in the ground.