Haden is my favorite bassist. I realize that William Parker, Richard Davis and Ron Carter may be technically superior, but Haden gets to me. There are a few different reasons why.
1. Deep resonating soulful slow playing. Try Prayer from Keith Jarrett's Death and the Flower.
2. Bass that feels like strummed flamenco guitar, very Spanish feel. Hear Paul Motian's Tribute album.
3. Funky grooves that often incorporate #s 1 and 2. Ornette Coleman's Law Years from Science Fiction, Keith Jarrett's De Drums from Fort Yawuh.