I don't use Vodka in my tinctures. I use Ethy alchohol. I use 100% pure grain alchohol. This is the type of alchohol recommended by Scott Cunningham in his incense, oils, and brews book. It was also the type of alchohol recommended in the bookKitchen Witchery
. For me this works rather well.
I've heard of using Vodka basically for tinctures intended to be drank. That would make sense. Though you would want to get as high a quality Vodka as possible for the most powerful effect. Most medicinal ticntures I believe are made with Vodka or another liquid. Some may use Rum if that is their preferred liquior. It just has to be I think at least 80 proof or so.
The tinctures I make are not intended to be used internally (as in drank or ingested) but topically as a perfume, an anointing liquid, or even as liquid incense. It burns like incense without the smoke. These are also magical tinctures basically designed to be bottled spells ready to use in an instant.