If I'm drinking it on the rocks. I would select Vox or Kettle.
of all premium vodkas, Ketel One is the dirtiest. and i don't mean that in a good way.
do this: take a glass of Grey Goose and a glass of Ketel One and leave them on the window sill until they evaporate. you will notice that one glass will have a lot of stuff dried onto the side of the glass. that stuff was dissolved in the vodka, but will not evaporate. that shit is the impurities that come from cutting corners in favor of cost.
absolut is overrated. they benefit from incredible marketing, yet they use column distillation, and claim to 'triple distill.' it is a lie.
Grey Goose, Chopin, Belvedere and the true Ultra Premium vodkas use pot stills, and filter the alcohol in between the separate distillation processes. this yields better product, and justifies the more expensive cost.
Goose, IMHO, is the best. they use four different grains, it's triple distilled, and filtered through Champagne limestone. however, if i'm mixing, i would use Skyy. #1, it's made in the U.S. #2, it's relatively cheap, and #3, they use pot stills and triple distill.