Under the given assumptions, Mamiya 6. I'd actually prefer the original to the MF version I have - I don't mind the more cluttered viewfinder too much, but it *can* be irritating. The camera and its three lenses fit into a small bag (ONA Bowery) - along with an additional roll of film, too. Its only downside is its bulk - it may be compact for MF, but it's quite a big camera nonetheless.
That why there's a couple more contenders I have to mention here: Leica M4-P (I don't know why I prefer it to the clearly more polished and full-featured M6 TTL, but I do - it just feels right; if Leica hadn't pasted its name all over it, I'd like it even better), Nikon FM3A (what a camera!), Zeiss Ikon Super Ikonta 531/16 (great shooter's camera, very well thought out - and still really compact for MF rangefinder), Voigtländer Bessa RF with its Heliar lens (a tad fiddly, but so very ewarding to shoot - for its day, a revelation).
M.