It is difficult to say which is the more fattening of the two. A typical recipe for brandy butter contains less fat than thick cream, but more kilojoules, because it has quite a high sugar content.
You could always substitute a reduced-fat margarine spread for butter when you are preparing brandy butter, but that would be defeating the purpose of this rich indulgence. If you enjoy such luxuries in small amounts, and only on special occasions, it is probably best to let your tastebuds decide which is preferable.
** Asian Recipes