As far as I can tell, weight percent is standard, unless you want or need something else. But there are different ways to do the analysis. However, the most accurate answers come when one uses a real standard, as opposed to the preexisting, or within software standard, which can be 25 or 30 percent off the mark.

It is preferable to present both wt% and at%. How you use the data depends on what you want to show. If you want to identify the presence of a compound, the use of at% will allow you to obtain the chemical formula. If you are checking elemental levels in an alloy, then wt% is used.