The larger the container, the longer the water will be within safe parameters for your Betta. If you ever want to upgrade a tank, I recommend this: http://www.petco.com/product/118200/...arium-Kit.aspx
It comes with a filter and at 1.5 gallons, is still small enough to fit just about anywhere but provides that extra room and water. The filter isn't going to last forever but for the convenience and nice look, it's a decent deal.
Just be sure to do the recommended water changes every week for bowl sizes you have now. This will help prevent future fin rot and all sorts of other health issues!