rule of thumb: 1 gallon of pot size per 1' of top side growth. basically a 5 gallon pot at finish.
but another member here skunk who knows his shit goes up to a 7 gallon. He gets some nice sized monsters.
I keep mine in a 3 gallon until 2 weeks before flower then transplant. Easier to manage for size for me.
I'm mostly a Hydro man, but back in the day, I used to grow in dirt. I've always been under the understanding that the less you handle a plant and move it's roots around, the less chance there is of hurting it.
That said, I think you should start off in your final container. I bought a cheapo hand truck with air tires and used it to move all my plants if they needed it. That way you won't kill yourself or your back.
The method of growing has everything to do with it as well. If you're using a drip system, then a 5 gallon will be perfect for a plant you'll take to 6 feet tall. The roots don't have to grow as much bulk because you're providing nutrients to it.
If you're watering by hand, then the plant will use every bit of a 5 gallon container because your nutrients will be dispersed evenly throughout the entire container and the plant will "reach" for it with it's root system. A 7 gallon container would be a safe bet.
Good luck and let us know what you use. We can all learn from each other.
Its all in how you transplant. If you do it right the plant won't even notice. Key is gently and lossen the soil lightly around the root mass (do this at night under minimal light roots don't like light). put it in its new home and water gernoursly. I do this as I don't have the space to keep 4-5 (5) gallon pots around. but avoid transplanting if you can. Stoney is right they don't like it much. but don't do it between the 3rd and 5th week of veg.