Do good power cords have to be stiff?

@tom6897 excellent point- many years ago I had a pricey balanced cable that was poorly terminated to the point that one leg broke off. I undid the Neutric connector, pulled back the tech flex, pulled back the company's own cable cover only to find that it was Belden cable. Nothing wrong with Belden, but it was a belden cable all dressed up.

@stereo5 The 7 gauge Pangea is ridiculous- had one years back. 

Unless your equipment is very poorly designed, I don't think you should be able to tell any difference between any power cords, assuming a decent construction baseline.  I can't tell a difference in my system, and the only blind test that I know of confirmed my experience by a guy who has a million dollar system. . . But buy whatever you think will work for you. . .

Shunyata makes excellent power fiords and the have an EF (extra flex) version that works very well