Top Three:
Osage: Most interesting and fun to work with and excellent (best?) self-bow performance when finished.
Hickory: Highest quality to find in board form (IMO), usually the easiest find and to work with, cheap to buy and extremely good performing self-bow.
Ipe: Hard to work with due to density, some people allergic to oils/dust, use only as a core for backed bow; however, EXTREME HIGH PERFORMANCE (just finished latest bow, BBI and it is hitting my highest arrow speeds ever).
Disclaimer: 1)Haven't worked with Yew yet, so no opinion at this time. 2) Mulberry is another big favorite but hard for me to find.