I am sorry, i am not much of a bar tender, but smirnoff sits well with different flavors for me. And there is a new one out that has all the flavors mixed, i think its called twist. so try that.
The Smirnoff has a real strong sugary taste. Would probably mix well in a drink. The Stoli is my fav, the vanilla flavoring is a lot more subtle, probably your best bet for a martini. Remember you get what you pay for.