Some of the world's most prestigious restaurants serve their best Cognacs in a gigantic 'ballon' glass.  The aroma of the Cognac rises straight to the nose, thus aggressing the smell.
True connoisseurs choose a smaller glass in a tulip shape, Containing 13cl, it should only be filled with 2.5cl.  In such a glass the aroma is concentrated before revealing itself steadily, allowing time to discover its subtle fragrance, observe its delicate color and mellow before even sipping it.