Which is a better focal length for fashion photography: 50mm or 35mm? I have Nikon D5100 and Nikon D7000 and I'm interested specifically for ramp walk.
I would use a 50 on your crop sensor cameras, it will give you a good position and good range to get a variety of shots from different distances as the model walks. The 50mm will in fact be around 70mm on your camera.
The 35mm has some level of distortion compared to the 50mm so if you are not prepared to adjust this afterwards somehow then a 50 would be your better bet.
Failing this you could use a normal telephoto up to about 105mm but you may have an issue with getting enough light so either use a flash or up your ISO to around 12000 (auto-max), your d7000 should be fine with that level.
On a APS-C Camera (as your Nikons are) I would recommend you 35mm (KB 56mm) if you want to have a "normal" (like eyes see) looking image. With 50mm (KB mm) you will get a light tele-zoom effect. On full-frame camera take 50mm.