Always cardboard boxes for me. Bought 0pastic for quite a while, but in the meantime AI get better quality milk in cardboard for less money than in plastic. And the glass bottles here are just stupid: expensive, single use with deposit. Neither good for the environment, nor for my time resources.
The cardboard milk here, being "UHT" (ultra high temperature) treated for a long shelf life doesn't taste the same. For many preparations it doesn't really matter, but for some it does.