If your climate is good and long you could grow some huge plant.... If you live in Southern California you should do 100gallon pots because your plants will become monsters... you should also be planting them soonish
If you live where its cold and cloudy than dont go too big because it's just a waste
I may go from ten to fifteen gallons, but have a limited area for good sun and security, so I'll likely go for variety versus a few monsters in larger pots. They can still get pretty big if fed right
If you are considering 10gal vs. 15gal I would say just go for the 15 and trim back. The only reasons I would go with a 10gal is if I was keeping the soil costs down and handles on the pot for moving. Other than that it's 15gal or bigger for me.