ask a question for AUG, BB's

which BB's is more suitable for AUG, .20g? .25g? .28g? or .30g? my friend have a AUG, he used .20g, i think .30g is better than .20g.
A few days I intend to buy a airsoft gun, i like quite, so, which is more suitable for me between sniper and AUG? I hope you can give me a idea.

Simple terms the heavier the BB the more accurate it'll be since wind will effect it less than a lighter BB. A "drawback" to using heavier BB's is that it'll lower your FPS however performance won't suffer, in fact the slower moving heavier BB will transfer more kinetic energy than a lighter BB travelling faster. You want to be careful though about which weight you're using in your guns, using .30's isn't needed in most AEG's, GBB's, or stock "sniper rifles".

A spring rifle will almost always be quieter than an AEG, but unless you know what your're doing and don't mind waiting then playing the sniper role is very fun. Plus a new flash suppressor can sometimes drastically change the guns sound signature to either louder or quieter.