Wacom Cintiq, because it has to be plugged into a beefy computer and costs $2,800 on its own is nearly twice as expensive as the Surface Studio, all told, and I don’t know if you’ve ever used one, but they’re archaic. They’re big and bulky, don’t have the really cool adjustable form-factor of the Surface Studio (you can tilt, but can’t easily transition between regular monitor and studio positions).
Yeah, the pen works great, but the software installation process and UI and driver support is a nightmare. Integration with the rest of the OS and apps is also a bit lacking.
The Surface Studio isn’t some niche third party add-on. It’s Microsoft’s flagship Desktop computer — the first one they’ve ever offered, and they’re trying to make a splash with it. And unlike Apple computers, the Studio runs on a touch-first OS UI, so using the OS and other apps with the Studio touch UI will be much smoother than it is with the Cintiq.
At nearly $6k, no the Cintiq is certainly NOT serious competition for the MacBook pro (being just a glorified touch-screen monitor, it’s not competition at all, but an accessory), but at $3–$4k, the Surface Studio will certainly put some pressure on Apple. I’d put money on it.