For the record, I have never touched either. Having said that, I would go the Zeiss Ikon.
Why?
Because it has a brighter viewfinder. Because the way you adjust exposure compensation is genius. Because it's smaller and lighter. Because the rangefinder baselength is longer.
I bought my M4-2 because I wanted something tough and manual--no electronics whatsoever. I use the camera to take pictures of things that give me time to think about exposure. If I wanted to shoot candids or street shots, I would probably go for a camera with AE--something small, lightweight, and inconspicuous. It would be the Zeiss Ikon, for sure. It costs less, and I don't care that it's not as heavy-duty as the M7 because I don't see myself ever treating it poorly (that's what the M4-2 is for!).
Just my 2¢.