I just chose the 6D, check out the "So who's buying a 6D?" thread, lots of good info there.
IQ is looking really impressive with sample images release so far. There have been RAW files also (there's a thread with a link, but I haven't looked at them yet). So you can check the IQ for yourself pretty much.
Ruggedness is non issue, it's constructed like a 7D except the very top of it due to WiFi and GPS receiver being built into the camera.
Just a thought, if you shoot on a tripod from low angles for your vintage cars, as I do for my motorcycle shots, I think the remote app via WiFi would be a killer feature, as you can position the camera any which way and focus with live view without having to lie on the ground trying to look at the LCD screen.
That alone, plus the fact that its 4 years newer, was enough for me to go with a 6D.