is almost always better for ALL kinds of tea — teabags usually contain low-grades of tea that are neither as flavorful, nor as beneficial in terms of nutrients and thereby health, etc.
Particularly with, some of the best/most expensive variants in the world come from . Very rarely will such high-quality green tea be packaged in tea bags for consumption. I have personally found the green teas packaged by Twinnings, Fortnum & Mason, etc. to be of far lower/inferior quality than some boutique offerings provided by tea-estates among other sellers such as , Teavana (which is now losing its lustre because of Starbucks), etc.
Lastly, if you do plan to use loose-leaves, be sure not to over-brew the tea — this results in a bitter flavor which is not representative of the tea and can be quite displeasing to the palate. A good glass teapot with a removal infuser usually does the trick here.