I owe a couple of the Akasa ProSlim cables (rebranded as DeLock?) and they're quite nice. The're plenty flexible, have clips and are sturdy. The others, I'm afraid I cannot say anything about (couldn't find info about the Darkside cable).
The Silverstone is as said above very flexible. I've really enjoyed working with them. The heads seem slightly fragile, but I haven't actually had one break for me.
It also comes in black, if you don't care for the "noctua effect".