The most flattering lens to use for portraits depends on the desired result and the specific characteristics of the lens being used. Generally, a lens with a longer focal length (e.g. 85mm, 105mm, 200mm) is considered more flattering for portraits because it can create a more pleasing, natural-looking perspective and compression of features. These lenses can also help to minimize distortion and produce a more cohesive image. However, lens choice ultimately depends on the look you want to achieve and the specific characteristics of the lens. It is a good idea to experiment with different lenses to find the one that works best for you.
Canon 100m f.2.8 Macro lens