Both of these focal lengths are good for shooting portraits. It ultimately comes down to what you’d like to capture in the picture. An 85mm lens is typically considered a classic portrait lens. It allows the photographer to be farther away from their subject and gives a very flattering field of view. A 50mm lens means you have to be closer to your subjects as you shoot, or you’ll end up with more of the setting in the photo. The wider field of view means it’s a great choice for environmental portraits. A 50mm lens is typically more lightweight and cheaper too, which are advantages.