Fabric pot

I'd go with the 5gal if you have the room. Fabric pots tend to dry out real fast on the exterior and its kinda shrinks the available growing area internally. I'd also put it in another pot with room aorund the sides to take full advantage of the air pruning and to help protect it from direct sun, most fabric pots I see for sale are black/dark and that can heat up the root mass/medium to much if in full sun. typicality more roots = bigger plant, so bigger pot would make sense. Some plants tap out early though, how big it can get will depend on growing style and genetics. Also width of the pot should be equal to or more then the height of the pot. Good Luck!

I only grow autos and I only use fabric pots - they're the BEST... I've grown in both 3 gallon and 5 gallon just to find out which was better... would 5 gallon pots help grow a large plant was my main question and the answer is: no. What they DO do is consume more water, more nutes... so I've now gone back to growing ONLY in 3 gallon pots. But if you've got a couple of seeds of the same strain, do a test yourself... grow one in a 3 gallon and the other in a 5 gallon - see which one YOU like the best. Me? I'm sticking with the 3 gallon! Indoor or outdoor, autoflowers are pre-programmed to do things at certain times... and they're pre-programmed to be a certain size as well... from my experience, a larger pot does not make a larger autoflower... photoperiods, yes, but not autos. Compare my diaries with FreeCain's (he doesn't have any). Happy autoflowering!