The only liquor I don't like is Gin... I may need to try it again but my whole inheritance from my parents came down to a big bottle of Tanqueray. Ended up giving it away to someone else...
I've long known there are big differnces in Islay or Speyside versus Highland Scotch, or even different brands and styles of bourbon, but used to think "gin is gin". Then a friend opened my eyes to that, there are actually substantial differences in something like Tanqueray (really only good for G&T) and Hendricks (better G&T) or Bombay Sapphire (my fav for martini). So, if you tried Tanqueray and didn't like it, try Sapphire or Hendricks, you might be swayed. I also like Beefeater, but it's too similar to Tanqueray to suggest it as an alternative, there.
If I recall, Tanqueray and Beefeater are traditional "London Gin", whereas Hendricks is Scottish and something a bit different. It's become one of my favorites. I never looked to see where Bombay is made, but their Sapphire (blue bottle) is definitely something a little different from their regular distillation (clear bottle).
The nice thing, at least in PA, is that the liquor stores still have little single-serving bottles behind the register. So, you can buy three different brands for just a few dollars, and do your own taste test in your favorite recipe.
As for Tonic water, I used to drink a bunch of it before I retired (worked great on leg cramps) I worked outside and usually didn't have time for water breaks. Got to the point where I had to force water down... but still had cramps at night.
Same. All liquor is dehydrating, but it seems G&T is uniquely so. Maybe Tonic is a diaretic, in itself?
If I work out in the sun all day, sweating and losing water, a G&T in the evening is a pretty good way of ensuring a 3am leg cramp.
You might as well just wave a closed bottle of vermouth over your gin, or just whisper the word “vermouth” over your drink, at that point. 
