For daily consumption, I'd honestly just go with the discount brands. The mineral content is regulated across the board, and your body won't notice the difference between 50-cent and 3-euro water. The only real factor is whether you like the taste - and it's just cheaper to figure that out if you don't want to throw a lot of money away.
But what's interesting is: some brands really do taste different, not because they're better or worse, but because the mineral content varies. San Pellegrino, for example, has more minerals than a lot of discount options, which is why it tastes more intense. That's purely a matter of taste - not healthier, just different. If you're drinking large amounts daily, it just makes more sense to save money with the cheaper varieties.