I'd always heard or read (probably most often from the Hitchhiker's Guide series) "gin and tonic." This made some sense as the gin would suppress the bitterness of the tonic. A properly made gin and tonic doesn't taste much like anything.
But recently I'd been hearing "vodka and tonic" which was a bit puzzling as vodka is supposed to taste like... well, nothing. So it seemed odd to affect the tonic with something without any flavor beyond that of alcohol.
Ah, but what is gin? It is flavored vodka. Vodka flavored with juniper seeds. I've heard folks say it "tastes like pine needles" but that hasn't been my experience. Either I just plain don't register that flavor very well or else I've either had really good (or really bad) gin when I've sampled it. I've had gin and tonic and like such on occasion.
Maybe sometime I'll try simple vodka and tonic and see if it tastes much different.
The scotch and whisky responses to the last post puzzle me a bit, but I suppose anything that can be/is mixed with one liquor is eventually mixed with others. Also, if one really does taste gin as pine needles, I can certainly see going with something else.