interconnects vs speaker cables vs power cords - which make the biggest difference?

My experience has been that, the speaker cable upgrade made the biggest difference.

Since interconnects are the earliest in the chain they should make the most difference but it is really system dependent and also cable dependent
Alan

I tried using Harmonic Technology Pro-9 speaker cables on an Almarro tube integrated (20 wpc). The sound was thick, slow and no treble. I changed to some Nordost Blue Heaven I had on hand and the sound was transformed! Literally night-and-day. Interconnects are designed for a (relatively) stable environment (line-level voltage).
Power cords? I've  never had an "ah ha!" moment. All-in-all I'd go with speaker wire makes the biggest difference (note: The Harmonic Technology is wonderful with high-power SS amps).

IME power cables made the most difference

 It really depends on the system. But in general, power cords and conditioners make the biggest difference. Then speaker cables and lastly interconnects. But again it depends on the system. I have found mixing brands of speaker cables and interconnects can deter the performance of both. Synergy is the most important thing. There is no perfect or best  cable for everyone.