with the Df release, I believe this discussion is somewhat relevant again
although one of the key selling features is the size of the Df, it is actually barely smaller than the Canon 6D and only a few grams lighter.
http://camerasize.com/compare/#380,495
and with the 6D having user interchangeable screens and the ability to mount various different mounts, it arguably has more flexibility with older lenses
the 6D does have worse non-center point AF, non 100% VF and the image quality is probably not as strong as the Nikon sensors
i just purchased a 6D recently and so far i am happy with it. i really appreciate the "gadgetry" of the 6D!
-Wi-Fi remote control for tripod work (works even in infrastructure mode, i.e. you can be in a totally different room)
-GPS geotagging and logging to make KMZ files in Google Earth (who doesnt want to know where their photos were taken on a trip?)
-i believe the live view implementation on Canons are done better than Nikon, especially with respect to Exposure Simulation and having Histograms
-having updated primes with IS is fantastic, i believe Canon really should be commended for that. at the new lower prices of the IS primes are great value. compare the 35mm f2 from Nikon to the new 35mm IS as an example.
with the retro design Nikon is getting all the attention but the 6D could be a better choice for a lot of people!