If your pretty serious about flying/ competing, I'd get the 9C. I use one and it has been all I have needed. I looked at the 7C but figured I would have wished I bought the 9C.
Another possibile reason to go with the 9C is Spectrum or spectra may be the frequency of the future and Futaba may just sell a module for the 9C, to convert it?

Buy what your budget allows, Your TX is used on all your planes.

Food for thought:
I told a Masters pilot " I will never spend $1200-2200 on a radio", he said "thats what we all said".