I’ve found that going up a size in hosiery is often a good idea if you’re regular height or taller. For example, if you usually wear a medium, try a large. Or if you’d normally fall into the “C range”, size up to “D”.
Going up a size reduces the stretch, making colors more even and reducing pattern distortion. It also lowers the risk of laddering and increases the longevity of the hose, which is particularly good if you prefer the better quality, more expensive brands.
Saggy hose is unsightly, so don’t go up more than one size. If you are petite the stretch is already less than average, so you may not need to size up at all.