Burn them both.....
the international is,I belive, basically the ford 6.0 motor, so that's a roll of the dice and the C7 is, well, a C7. If the C7 has been maintained I would think that might be the better motor, but someone with a lot more knowledge on both of those engines should chime in soon I would think.
I've had both engines in two different trucks and I never was impressed by either one. The 6.0 I had was in a 550 that I bought new and it was meticulously maintained, always had clean fuel, and never idled, and I've never had an engine leave me dead on the side of the road more times than that one, I had a C7 in a freightliner FL80 10 wheeler that I bought used with 80000 miles on it but I'm fairly sure the maintainance on it left a lot to be desired, since I had to replace the motor in it shortly after I bought it.