I based my answer purely on your poll question:
What is your fave yarn to work with?
I enjoy using ALL yarns, because they all have their function, depending on what I want to make.
But, the yarn that makes my hands happy when I'm knitting is good old fashioned, worsted weight WOOL. It just seems to flow nicely, and makes such a pretty fabric. The stitches just seem to "stand up" proudly.
When I've knitted swatches of different yarns, and compared them, the wool swatches always look so much nicer and more professional.