The "Pet Peeves" thread has taken a turn toward vodka, so I thought I would give it a thread of its own. As noted, most vodka is made from grain and although there are a few potato vodkas out there, mostly from Poland, the vast majority of the vodka consumed is from grain. The potato brands are not big sellers.
Most domestic vodka is made from corn. Imports may contain some percentage of wheat or rye, but corn is pretty popular there too. Although market prices can vary, corn is generally the cheapest grain in terms or its alcohol yield.
Most domestic vodka is made in one plant in Iowa and shipped by tanker to various bottlers. Some imports are actually buying this U.S. grain neutal spirit (GNS), diluting it with their water and selling it here as an import. I can't necessarily say which ones because it varies. The international GNS trade is a little like the oil trade. It's a commodity. You don't necessarily know where it originates.
GNS typically leaves the still at 195 proof. In other words, it is as much pure alcohol as it is practical to make it. Alcohol is alcohol. All alcohol (that is, all ethyl alcohol) is the same. It has no taste except the "taste" of alcohol.
I have been told that some imported vodkas distill out at less than 195 proof, which means there could, conceivably, be some taste difference in the final distillates.
However, no vodka is sold at 195 proof. Naturally, it is most efficient to ship the bulk GNS at its maximum proof and to dilute it to its sale proof at the point of packaging. Here again, a lot of domestic vodkas are exactly the same because the same company is bottling them and using the same water to dilute them. Heaven Hill, for example, "makes" a number of vodkas, for themselves and other marketers. I put "makes" in quotes because all they do is pump it from the tanker into a tank, dilute it with water to the apppropriate proof, and bottle it.
The point is that the extent to which one can taste the difference between one vodka and another is because there are differences in the water used to dilute it from 195 proof down to 100 or 80 or whatever it's sold at. In other words, the most expensive bottled water in the world is the water component of imported vodka. The only caveat to that would be those vodkas that are distilled out at less than 195 proof which may retain some flavor in the distillate, but no one can tell you which ones those are.