I am currently using 3 and 5 gallon pots for my photo period plants. I would heed SoOrbudgal, as she prefers autos and knows them well.
Myself, I'm enjoying the experience I gain from every grow. You'll find GWE generally indicates the bigger the pot the bigger the plant. My first grow was autos and they didn't get very big in their 3 gallon smart pot.
My opinion mirrors Woodsman67 - Give it a few weeks,