Everything varies based on every aspect of the grow. Lighting, strain, medium, conditions, experience etc. I've grown the same strain in 1 gallon, 2 gallon, and 3 gallon pots. There was a difference between the 1 gallon and the others. 2 & 3 gallon not much difference, except the 3 gallon took longer to dry out so there was less opportunity to feed, and correct issues. 2 gallon is the best overall IMO. Though if you're we're growing a particularly large auto 3 would be the way to go.
My advice is to dedicate meaningful time researching on this site if you are interested in autos.