If you want the biggest possible roots from a potted plant, I would go with straight into the final pot, or putting the coco pot into the final pot pretty much as soon as the seedling breaks the ground. It's surprising how fast that taproot can grow.
Joe's right that for a taproot it doesn't go as deep as other plants, and the rootball he's showing there is what I get when I plant straight in the ground outdoors.
For what it's worth, this is what I got from a couple of autos this summer planting straight into the final pot.