Hard question to be honest. There are simply too many factors and things that are at odds with various designs that make it difficult to pick a single favourite.
Currently the film collection stands at a Mamiya C330, which I am loving a lot, and a recently added Busch Pressman 4x5, which is looking like it should prove very enjoyable for the odd times I will get out with it. But at the same time I still very much love my canon 7D and the kind of shots I've been able to produce with that. Sure, they're nothing like what I get out of film, but isn't that kind of the point of having various formats and styles of camera on hand?
The thought process and state of mind is different with various cameras, and I like that.
I guess my lame copout answer would have to be "The camera that does the task I have at hand, and that I can afford." - I would love to own a Hasselblad system because they look and feel so slick, but I settled on the old TLR C330 instead because I got it and lenses for far less. And honestly I simply can't complain about the images I can make with it. I could spend more on a 'better' 120 6x6 camera. I could upgrade my digital bodies to something not several generations old sensor tech. I could pour more money into 4x5... But pushing too deep in any one area would rob all the others of any kind of budget. And I'm happier having more options.
, me thinks there is a pattern developing here ... 
