Design compared

Compared to Canon EOS 60D

The EOS 6D takes its design cues from the EOS 60D. In fact, there is very little in the way of body size, control layout and styling to differentiate the full frame model from its APS-C sibling.

The EOS 6D is slightly taller than the 60D, due to the extended hump of its full frame prism housing. The monoaural microphone position has been changed from above the model logo on the 60D to below it on the 6D.
While the button layout has been tweaked, the available controls remain identical. The EOS 6D does adopt the live view/movie mode button and switch combination found on recent Canon DSLRs. What it loses is the 60D's articulated rear screen, which shaves some millimeters off the camera's depth.
In what should make for a seamless transition for 60D upgraders, the arrangement of the AF, Drive, ISO, metering and top plate illumination buttons remains identical. The EOS 6D forgoes a built-in flash, as do Canon's other full frame cameras. On the 6D, the individual scene modes have been moved off the mode dial and are now selected via the rear screen menu.

Compared to Canon EOS 5D Mark III

The EOS 6D slots in below the 5D Mark III in the EOS lineup, and not surprisingly gives up some features in comparison. The 6D's much-simpler AF system is perhaps the most glaring difference, but it also shoots at a slower burst rate. However, 6D owners do get built-in Wi-Fi and GPS and interchangeable focusing screens.

This front view shows just how much more compact the 6D is compared to the 5D Mark III. The overall family resemblance is striking though; about the only obvious difference is that the 6D's depth of field preview button sits on the underside of the lens throat (not visible here) rather than the front body plate as it does on the 5D Mark III.
There are a lot of similarities from the back, but some key differences too. The joystick multicontroller on the 5D Mark III is replaced by a 60D-like 8-way pad inside the rear dial, and the column of buttons down the left side of the LCD have moved to its right, with the upper two disappearing altogether (Rate and Picture Style/Effect).
From the top, the 6D's slightly lower-level aspirations are reflected by the mode dial, which is more-crowded with extra automatic modes. The buttons along the front of the LCD panel also serve only a single function rather than two, and there's no customizable M.Fn button beside the shutter release. But overall this is very familiar EOS stuff, and the two cameras behave very similarly during normal shooting.

Compared to Nikon D600

The EOS 6D's most direct competitor is, of course, the Nikon D600. The cameras share similar dimensions but differ significantly in control layout.

The EOS 6D and Nikon D600 both reflect the longstanding - and often directly opposing - design aesthetics of their respective companies. Canon's front dial rests behind the shutter button, while on the D600 it sits in front. The 6D features only a depth of field preview and lens release button on the front of the camera, while the D600 also includes custom function, flash compensation and bracketing buttons along with an AF mode button/switch combination.
Both cameras are nearly identical in width and height. The EOS 6D's button arrangement appears more sparse, with the left side of the screen devoid of control points.
The Canon EOS 6D is slimmer back to front than the Nikon D600, lacking the latter's decidedly beefier and deeper hand grip. The D600 includes a built-in flash and its power switch is integrated with the shutter button for one-handed access in the shooting position. Both cameras feature a lock on the mode dial to prevent accidental operation.