My favorite material? Hard to say. I love Bloodwood, Wenge, Yellowheart, Quilted Maple, any highly figured wood, and Walnut. I also love the look of certain acrylics, but they are not as much fun to turn.
I recently acquired some awesome looking Bethlehem Olivewood that I look forward to turning. (Thanks PensByBud)
There are also many other materials that I want to try.
Way down at the bottom of the list is Oosick. I think the name says it all.