One of the simplest and best mixed drinks ever devised, hence its lasting popularity.
To serve as a Highball use a smaller 10oz (295ml) Highball glass...
I always found a G&T to be quite an unbalanced cocktail, for my taste anyway. Whilst I ultimately think I just can’t get along with the tonic water in general I have settled on a 1:1 ratio which I think achieves a nice balance of complex aromatics, bitterness and tartness from your preferred citrus garnish.