If you weigh around 63 kilograms, it fits comfortably in the middle, has a pleasant fit, and the cotton is good without any discomfort, size medium

I rate it as "very good" and not as "excellent" for two reasons:
1. Its fit is low-rise. It doesn't look good in the photo. It sits lower in reality than it appears. Thin men won't have a problem, but those with a belly (i.e. pot-bellied or chubby) will have an issue with the waistband because it falls on top of the... "rebound" (or lower surface) of the belly. Comparing it to a similar boxer from Celio (if you can find it anymore), it has a lower rise and doesn't hold as well.
2. The fabric is pleasant and stretchy, but it doesn't hold up well. After 3 washes, it starts to fray annoyingly.