It could be either. Even with some troubleshooting, there are problems with both that will give the same indications. I will venture a guess though that if you hear absolutely nothing at all, not even the solenoid click when attempting to start, it is something between the ignition switch and the solenoid and not the starter.
You can just about narrow it down by trying a temporary jumper.
Two words of caution
1) Put you car in N if 5 speed or park if auto because doing this jumper thing I am describing bypasses the N safety switch and the clutch switch so be careful, double check it, really.
2) Keep the keys out of the ignition while doing this and just in case, take the rotor out as well to keep it from actually starting.
Place a small jumper wire between the positive on the battery and the small threaded stud on the top of the solenoid. The car should crank and keep cranking the whole time this jumper is attached. If you do not hear the solenoid click, the solenoid is bad or the ground for it is bad. If the solenoid clicks but you do not hear the starter engage, it is the wiring to the starter, the starter itself, or it could still be the solenoid.
If the solenoid clicks and the starter turns over fine then it is something from the ignition switch to the solenoid which includes the clutch switch.
If you are not sure what small screw terminal on the solenoid I am referring to attaching the jumper on, look through a manual or a wiring diagram somewhere. Don't just start touching things with a live jumper wire attached to the the battery.
Being an intermittent problem makes things a little tricky. The next time it does not start for you, listen for the solenoid click, that is the major thing for narrowing it down. There are a lot of things that click when you turn the key, have someone close to the solenoid to make sure.
Report back your results and we can take the next steps!
Don't forget to put the rotor back in