Vodka tonic tastes like bubbly slightly sweet lime water. It is a tad bitter at times, but very smooth going down the throat. If good vodka is used all you can taste is the tonic water. That's because vodka by law is a neutral spirit, meaning that it can have no discernible taste.
For starters, a true martini uses gin, not vodka.Beyond that, it is up to the bartender or whoever as to what kind of vodka you use for a vodka martini. That said, plain vodka appears to be most common.
I would recommend using this recipe to try making a vodka martini, http://www.foodnetwork.com/recipes/the-cookworks/the-classic-vodka-martini-recipe/index.html.
Yes, you can replace vodka with gin in a chocolate martini, but it will alter the flavor profile. Gin has botanical notes that can add complexity, while vodka provides a more neutral base. If you enjoy the herbal and aromatic qualities of gin, it can create a unique twist on the classic chocolate martini. Just be mindful of balancing the other ingredients to ensure a harmonious taste.
gin
It is a gin or vodka martini made with no vermouth
He drinks a vodka martini "shaken, not stirred."
A vodka martini is often made with 2 parts vodka to 1 part vermouth so 1 1/2 oz vodka and 3/4 oz vermouth.
Vodka Martini (shaken, not stirred) and in recent films, the Vespa Martini
A vodka martini
Martini's
Vodka Martini (shaken, not stirred) and in recent films, the Vespa Martini
Black Star Liner