I don't have Fuji GF670 and no Plaubel 67, but i have hassy and Mamiya 7 and GSW690iii and RZ and recently RB, out of those all the only cameras i will carry for sure are Mamiya 7 and GSW690iii and never look back, my Mamiya 7 is not working but it will be my first choice even if i have GF670 or Plaubel, and i carry GSW690 because this format is large and sharp and it is always blowing away my mind with its quality with any film i through in, B&W or color.
For medium format I use my Bronica SQ-B. A good and inexpensive camera.
For traveling light I take my Bronica RF645. Easy to handle, rather compact and light. Has a very good build-in light meter. And the glass is excellent!!
And did I mention the excellent rangefinder on this camera?
* I'm an analogue enthusiast, trying not to fall into the digital abyss.
* My favorite cameras: Hasselblad SWC, Leica SL, Leica M7, Russian FKD 18x24, Bronica SQ-B and RF645, Rolleiflex T2, Nikon F4s, Agfa Clack and my pinhole cameras
Mamiya 6 or 7 if you want interchangeable lenses and a very small kit. I love my Hasselblad too, but it's bulkier and requires a tripod more often.
Agfa Super Issolette (or Ansco Super Speedex is the same) if you can live with a single normal lens. These fold up nice and small and take excellent pictures with a look that is more classic than modern.
you don't have to be super-rich to own a Rolleiflex. For the money that a Fuji GF670 costs, you can get a nice Rollei 2.8F or maybe even a GX. If you don't have to have an internal meter, for less than half the price of a GF you can get a 2.8E (the reason I say no internal meter on the E is that the E is now 50+ years old and most of the meters in the E models are somewhere between less than fully accurate and flat-out dead). But the big question is your shooting style - do you think in rectangular composition, or are you comfortable with square? what about viewing style? are you comfortable with waist-level viewing or do you have to have the camera at eye level all the time? do you compose tight or loose? Answer these questions first and you'll be much further along in your decision-making.
I'm a huge fan of the 6x4.5 Fuji's for handheld travel cameras. Load it up with the 400 speed film of your choice and have fun. If I had the money, I'd do the Mamiya 7, but I'm not sure that the quality would be any higher except for the bigger neg.