The glass carboy and plastic carboy are the preferred fermentation vessel for many homebrewers. Glass carboys are easier to clean, and plastic Better Bottles are lighter and won't shatter. For more information on glass vs. plastic carboys, click here.
6.5 Gallon fermenters are perfect for the primary stage of beer or wine fermentation. The extra head space allows for the production of krausen on a 5 gallon batch of beer.
5 gallon fermenters are best for the secondary conditioning stage of beer fermentation. The smaller size eliminates extra airspace in the fermenter reducing the chances of oxidation which can stale the beer prematurely.