What fiber or yarn do you love working with?
For projects that will be going to children, parents of children, or people who are not knitters and will therefore not hand-wash a damned thing, I prefer Caron Simply Soft. It’s soft, it comes in a decent range of colors, and it isn’t too expensive.
For projects I intend to keep, I’ve fallen into coveting MadelineTosh and Malabrigo. Good golly, they’re expensive, but they’re soft and (in most cases) bright and beautiful, and frequently are kettle-dyed for a softly mottled look. Yum.
I should note that I’ve never worked with cashmere or pure silk…yet.