My absolute favourite is Monkey 47, with Fever Tree tonic, and a slice of lime.
I've got a bottle of Citadelle Réserve that I bought based on the rave reviews I've seen, but I don't really like the taste of it. It's certainly not bad, but it has some kind of weird aftertaste that leaves me meh.
Sapphire and Hendrick's are old friends I will always welcome.