The most expensive Vodka I've had is Grey Goose, to be honest I dont know where that ranks in the hierarchy of Vodkas other than its got a good rep and stupid girls will think you are a baller if you have it. Tito's is better than Grey Goose though, a lot better IMO. My buddy won Mixoligist of the year from Salt Lake Magazine just barely and he swears by Titos also, so its got to be at least pretty decent. It is also fairly cheap, not like Popov but you aren't going to spend your whole alcohol budget on it either.
But yeah, Vodka is little more than something to pour in whatever you have handy when you need to sneak something to me also.