The look and feel of your demo CD has a significant effect when someone picks it up and needs to decide whether to listen to it or not.
The audio quality of CD blanks does vary, but not enough to make a difference for a demo, unless the blank is faulty of course. The more significant factor is the appearence of the label side.
Firstly, if you want to impress, you must use a quality stick-on label,well designed and printed. The best labels are the ones with a photo-quality glossy surface. Those that look and feel like ordinary paperjust seem cheap.
Pay attention to sticking the label down evenly, properly, and withoutlumps caused by dust or air bubbles getting underneath.
Also, the CD blank should be just that – blank. Nothing looks worse thana CD with manufacturer's logo etc. covered by a label.
OK, you will have to pay more for your labels, but unbranded CDs usually cost less. It evens out.
Moral – it's your music. Don't make it look cheap.