Lime - Lemon is an aberration. No lime, well even cucumber.....
Tanqueray Gin for me when it comes to a G&T, loads of ice 25% tonic, the rest being the gin. Squeeze the lime before putting it in. If hard, 10 secs in the microwave 'juices' it up.
Have you tried Sipsmiths? - On the rocks with nothing in it other than a twist of lime for a pousse-café - it's that smooth.