the good quality stuff is a solid copper core, stay away from the "twisted wire" versions!
I wouldn't say one is 'good' and one is 'bad', just different uses, depending on your intended application. Twisted wire (stranded) is more flexible and less chance of internal breakage, one reason why we have service cord. Due to the chance of breakage, CG rules do not allow solid core wire less then 6 pairs.
Okay.. warning.. more geeky stuff ahead...
US standard telephone wire is black, red, green, yellow. Red/green being the primary pair, black yellow being the secondary, as defined by Ma Bell. This wire works good for RGB leds, since you can line the colors up with the leads on the led.
The white/blue, blue/white, white/orange, orange/white color combination is an offshoot of the 25 pair color code. This came much later in production, the original 25 pair colors did not have the secondary stripe. Originally it was just the white & blue pair, white & orange pair, the white being the first, the color the second. Technology is a good thing as now we have the stripe to help keep things straight.