I think I can easily say Shadowrun without a shadow of a doubt (sorry).
Shadowrun is one of those bizarre settings that seems to mash up everything. It’s got magic. It’s got high-tech sci-fi action. It’s got gritty, down in the streets with the trash, contemporary survival. It’s got cyberpunky fuck-the-system rage-against-the-machine politics. It’s got fantasy races and creatures. It’s got hacking and the matrix. It’s got cybernetics and guns out the wazoo.
While easy to simply label as ‘cyberpunk with fantasy elements’ it’s really much more than that and the setting, if not necessarily the game itself, can really lend itself to exploring themes that don’t come up too often in games like racism, poverty and social mobility. While ostensibly the game is focused around mercenaries, criminals, and wannabe revolutionaries, the setting works equally well for any number of contemporary stories, but with the added benefit that you can draw on these larger than life aspects from fantasy and sci-fi to really zoom in and highlight the things you want to examine in a game.
Numenera in many ways allows for the same because it’s so broad in scope, but where Shadowrun stands out for me is its roots in the contemporary, modern day world we know, while Numenera strips away that foundation. Numenera is exploring the new and the old from the outside-in, while Shadowrun for me is exploring it from the inside-out.
Even know Shadowrun is definitely my favourite, I have a few settings of my own devising that I really, really like and want to develop further into games of their own (or at least settings books to be used with existing systems).
Cybergothika is a setting that is post-post-apocalyptic. The apocalypse happened and was averted. Like Shadowrun it is rooted in the nearish future of the modern day and heavily features technological and biological augmentation, politics, while it doesn’t have magic per se, it has a certain paranormal angle to it that brings in demons and to a lesser extent psionic-esque stuff. The main themes of Cybergothika are that you are pawns in much larger games played by forces you can never hope to be equal to. You’re trapped, far down the ladder of power, but you can choose how you are used and you can try to climb that ladder as high as you can - or you can try to destroy the ladder entirely. As well as being trapped between powerful entities, you’re trapped between powerful, competing philosophies and beliefs. Cybergothika is a world rebuilding itself, while still dancing on the very knife-edge that cut it before and no matter what you do, you’re involved in one way or another - it’s up to you whether you want to try and benefit from that.
The Dockyards is my other setting which really excites me. It’s an anarchist state built on a massive floating platform in international waters. It’s a combination of directed construction work and old ships lashed and welded together, grown over many years into an international hub of crime, terrorism, morally unrestricted research and other terrible things. While effectively an anarchist state, it has a sort of caretaker (if not leader) that no-one has seen, called the Accountant. The players through seeking it out, being blackmailed or otherwise manipulated work for the Accountant as Dockworkers - people that solve the problems of the Dockyards no-one else will, while trying to keep their heads above the sea of corruption and amoral greed that live and operate there. The Dockyards is a terrible place, there is no law and the very worst of humanity can do whatever they please there. The rich and powerful go there to indulge in their sickest fantasies with slaves, from deviancies too sickening to mention to human hunts. Why has the worlds governments not tried to put a stop to it? They use it too, it’s a great disavowable launch platform for off-the-books black-ops and it’s an open secret that the Dockyards has access to potentially very lethal hardware - they could kill the ocean or fire a nuke and nobody wants to play chicken with a place that doesn’t even have a leader they can negotiate with.