Which one is best for the environment? I never though about this, but it is a good question. According to Natural Health magazine, if the wine is packed in Tetrapak containers, it is better to use than boxed wine.
Tetra pack containers are made using less energy than glass bottles. 10 Tetra pack containers use the same energy as one glass bottle. In blind tests, the wine tastes the same in bottles than in Tetra pack containers. Plus, shipping tetrapack containers takes less energy, and thus, they have a lower carbon footprint.
In other words, if you buy your wine for regular consumption and consume a bottle within a few weeks/months, you might be helping the environment by buying wine in a box, for example, Le Cask. If you plan to age the wine, though, you have to use the glass bottles.