Actually, I don't really like the taste of Polish milk that much, so I tend not to drink it by itself unless I'm dehydrated and there's no bottled water.
But for adding to coffee / tea / (and in rare cases) cereal, I would say łaciate. I think it's about 3-4zł for 1 litre. Biedronka's brand is also quite ok and roughly the same price.
The fresh milk sold in most supermarkets is quite good. But you can only keep it for a few days in the fridge.
If you are in Warsaw, the "mlekomat" on the back of Hala Mirowska sells really fresh milk - almost straight from a cow as it were :)
Sorry about taking so long to post a response, but better late than never...
It's probably this one zimnemleko.com/static/mikrofiltracja_zimnemleko?lang=en
It doesn't have the characteristic smell that most Polish milk has, it has no unpleasant odour and tastes clean and fresh, like British and US milk. It's filtered, like some premium British brands are too (this might extend shelf life).
It's a little bit more expensive than some brands but comes in a glass bottle. It comes in skimmed, semi-skimmed and full fat (which in Poland is denoted by percentages of fat, semi being 2%, full being 3.2%).