What are the best sounding DIY power cables and connections, opinions please ?

The next time your driving down the highway, look at those massive power line towers. 

1) the hot and neutral are separated, sometimes up to 100 feet apart.
2) capacitance allows high frequencies to pass, blocking low frequencies.
3) inductance allows low frequencies to pass, blocking high frequencies. The power coming from the wall is 60Hz. This is low. Capacitance is bad, Inductance is good. Separated +ve and -ve allows 60Hz to pass unimpeded.

4) there is not a single piece of multistrand wire in our grid system, nor is there a single piece of multistrand in any phono pre-amp made by man. It introduces a type of distortion caused by micro-arching between strands. Multistrand is more easily 'snaked' between components, while solid core is a pain to manipulate. Chose between convenience and power delivery.

There is a carrier signal in our power. It is how the electrical stations communicate. Capacitance allows this signal to enter your system, Inductance blocks this parasitic signal.

Power cords
Conduct a simple experiment;
buy 12/2 wire from your big box store
carefully cut away and discard the exterior jacket (run your knife blade along the center, making sure not to nik the insulated cable)
buy the absolute cheapest connectors you can find
buy electrical conductive paste
clean the bare wires, lightly coat in paste, attach connectors
spread the 3 wires apart (I know, I know, I know, this isn't to code. but we're audiophiles)

This is now your baseline. Now compare to store bought power cords. Draw your own conclusion.

If your find an apparent 'volume' loss, listen more carefully. You've actually reduced noise (specifically the carrier signal used by the power company).

Not one of you will try this. It's too simple, and cheap, and therefore must be wrong. 

Granny, thank you. You are correct in your observations. The baseline cable isn't yet perfect. It's the start. It's step 1.

Step 2
Go to ham radio sites. They use X and Y capacitors. These capacitors connect the hot to ground, neutral to ground, and hot to neutral. I can't remember which goes where, but when done properly, they completely remove the parasitic signal from the power grid. They also remove those 'things' a cable picks up (radio, tv, wireless router etc signals). You then need to carefully wrap these little things with electrical tape.

Step 3
I figure I better do this now.
Cardas makes a 12 guage Litz wire. Don't get their 9.5awg, it doesn't fit most connectors.
You will need a soldering pot, lots of solder, and patience.
Litz wire may have multiple strands, but it is not multistrand wire. We need to remove micro arching between the strands. Litz accomplishes this.

Remember to keep the hot and neutral wires separated. In a power cord, capacitance is the enemy.