I selected the D600, primarily due to image quality.
D3/D700 can't beat the D600 in IQ department. Compared to D3/D700 there are 2 stops of dynamic range, one stop of noise performance, more accurate colours. Also the electronics has been improved, there is less read and amp noise, no banding, no artefacts during long-exposures, and much improved hot-pixel suppression algorithms 24mp is a sweet spot on full-frame and the new Sony sensor is just amazing. Huge headroom for cropping (or much larger prints). If you are concerned about quality, you have to take the D600. Iin some areas it is even better than the D4 sensor (DR at base ISO and resolution) or D800 (less noise at pixel level). It is unfortunate, Nikon hasn't put the sensor to higher class body.
AF is a mixed bag. There are positives (focusing at f/8 - a big deal for wildlife) and negatives (less AF points, doesn't focus as well under low light). Also the shutter-lag is noticeably longer on D600 (and D700) than on D3.
As far as camera control is concerned. Don't trust the reviews that says the D600 has less control. It actually has a few nice tweaks over D700 (or D3) . Such as dedicated button for shooting banks, intelligent auto ISO, much better liveview, dedicated shooting mode wheel, dedicated BKT button, more customization options for Fn, faster switching of AF patterns, etc.
The only area where the D600 significantly falls behind is the build quality. It is plastic body, less durable. The eyepiece is significantly worse. Connector to grip is fragile. Plastic front panel and bottom doesn't feel confident enough. Also the doesn't qualify for NPS programme membership, etc.