Contrary to a lot of the posts so far… premium vodka is meant to be best for mixing as the whole point in vodka is that it is suppose to be tasteless. Premium vodka is filtered multiple time in special filters (carbon, etc) to make it as pure and tasteless as possible
I’d agree with this, I’m no Vodka connaisseur, but I just won’t drink Smirnoff red, it tastes funny, even in coke.
Smirnoff Blue or Absolut are only a couple of quid more a bottle than red and I’ll happily drink them with mixers.
No idea about supermarket own brands, I guess they vary from bad to rather good, depending.
Equally with a bloody Mary its probably less important, with tomato, tabasco etc, you’re not really gonna taste the vodka unless you’re making strong ones.