When in doubt, make a good power cord with garden-hose size 12-3. Most house wiring is 12-3 and bringing that same gauge right up to the amp can't hurt. From what I have seen, issues arise when the plug and socket are poor quality or not hooked up solidly to the wire. Those problems create noise and high resistance.
There's nothing wrong with integrated power cords that are well fastened (electrically & mechanically), have a good plug and use the proper gauge of wire. How can one go wrong with fewer contacts in the electrical supply chain? That clear benefit alone can outweigh many IEC so-called benefits.
What I like about IEC cords: They're easy to replace!
Since I like either fixed or IEC cords, you won't find me leaning towards either side. It's 6 of one and 1/2 dozen of the other in regards to pro's & cons.
Just remember this fact: You can have $100,000 wire and it won't mean a hill of beans if the contacts on either end of it are poor! Since IEC sockets are molded- well.... it is what it is.
If you ask me, it's time to move on!

What about a twist-lock setup that can be made to be self-cleaning? Or at least something like that...