I'd say the Steam Machine, but it's also hard to separate that from my hype for the controller.
Because a lot of what will make the Steam Machine so great is down to the controller and how it interfaces with SteamOS. The idea of being able to use the controller to wake from sleep, be booted straight into Big Picture Mode, then launch a game and be able to use those touchpads to navigate any rogue launchers or other annoyances, sounds like the closest to a console-like experience that i've wanted from PC for years. I've tried the whole "just connect your PC to a TV bro" thing and it just doesn't work. There is always a sticking point where you need to resort to using your wireless mouse and keyboard nearby. No thanks, that takes me out the whole experience, like an IRL Unreal Engine stutter in my gaming session.
I guess i'm also re-evaluating what I actually need my PC, the gargantuan box under my desk, for. I now watch movies on my Nvidia Shield. I browse the internet mostly on my phone and tablet. I spend most of my gaming time on consoles and handhelds now. I am caring less and less about the bleeding edge (which developers are barely delivering anyway), so the Steam Machine's lacking power doesn't really faze me. I grew to value that headache-free console experience more. But I do still want to keep a PC around for some games that simply only work well on a PC, like the RTS genre or Counter Strike 2, and for occasional productivity tasks like editing files or using Excel. The news I can just dual boot Windows and still get access to that is very welcome. The thing is also so tiny I can literally just carry it over to a desk and use it like a normal PC.
Retroarch will also make it the ultimate all-in-one retro device, which I thought Xbox Series X could've been before Microsoft blocked emulators. I already cancelled pre-orders for other dedicated retro devices like the SuperStation One because I feel the GabeCube will just do it better.
It's a near perfect device on paper. I've owned a Steam Deck so I trust Valve to deliver on all this. They are the one company I will always shill for.