I'd get a D7100 if it wasn't for the lack of the AF-ON button.
Having built my technique for movers around this feature- and found it to work brilliantly- there's no way I'm going back to letting the shutter choose when to focus for me!
Nikon must know that the AF-ON technique is used my many top flight pros (not me btw!). so if the 7100 was the 'pro' or 'ultimate' DX body, it would have an AF-ON button- just like the D800, D700, D4 etc. etc.