Simply saying that if you're in between sizes. Medium waste is "28-32" vs the large which is "30-34". Me being a normal 31 and being 160 and 6'1" I found it best to go large is sweats and sweatshirts becauss they will shrink in the wash and the medium may end up too tight. But if you're getting a dry clean only products I'd recommend to size downward to keep the ski fit without ever washing it.
This is true fresh out of the box (or bag), but with 1-2 wears, the medium is going to stretch to be the right size, whereas the large will be too big. Every time you wash your Escobars, the fit returns to being ideal, but after you wear them a few times, they start to stretch out. I'd say with the sweatpants, always go for the smallest size you can fit and still be comfortable.