I have some definite thoughts on this subject, without going into the heresy of calling a vodk .... . Oh, that's right, I said I wouldn't go into that.
So while I certainly recognize that you should be free to drink whatever you want, I ask those of you who like dirty martinis to consider the care that the master distiller went to to chose perhaps more than a dozen botanicals, in careful proportions, for the gin, and then what splashing in olive brine does to that careful balance. You might as well use bottom shelf domestic wino gin.
When Tanqueray Ten came out what, some ten or more years ago?, I fell in love with it. Much more up-front than my long time favorite, Beefeaters. So I used that in my martinis, except when I could score an even more in-your-face gin, Anchor's Junipero from my sister in California.
But after a while, I found these tiring, and so my wife and I tried a blind taste off of these two vs. Beefeaters, with Seagram's thrown in as well. Gin:vermouth @ 5:1. We did Tanqueray Ten vs. Junipero and Beefeaters vs. Seagrams, then the winner of each vs. one another.
The winner? Good ol' Beefeaters for its finesse without being wimpy. What I started with 40+ years ago! [Hey you kids, get off my lawn!]