As others have mentioned, it's system dependent.
With that said I'm going to answer your specific question and not get into other areas that you didn't ask about but others alluded to.
Power cords, interconnects and speaker cables in my opinion carry a signal or current of some type and can be used to tune your system (sound wise) to your liking. I find all three equally important.
If pressed to rank them in order, I'd agree with others that said:
1) Power cords
2) Interconnects
3) Speaker cables
With that said I'm going to answer your specific question and not get into other areas that you didn't ask about but others alluded to.
Power cords, interconnects and speaker cables in my opinion carry a signal or current of some type and can be used to tune your system (sound wise) to your liking. I find all three equally important.
If pressed to rank them in order, I'd agree with others that said:
1) Power cords
2) Interconnects
3) Speaker cables