There really isn't a best weathering technique, all those mention work well. It mostly depends on what kind of look you want to achieve with your saber and what you have available to you. Heavy sanding and cutting is often a more permanent weathering technique and can be easier to do in my opinion than using paints and some acids/oils to weather a particular color or pattern. Some paints and oils can be permanent, but most can be removed by light sanding or other acids and chemicals.
Here's an example of a weather done with sanding and cutting that I did on my Dominix v3. The pommel on the saber was originally silver and I sanded it and paint it with black spray paint.
