High quality German felting needles.  Generally, 40 guage needles work best with superfine Divine Wooltops, 36 guage needles work better with 20 - 28 micron felting wool and 32 guage work better with felting wool broader than 28 micron. 

Prevent your needles from rusting by wiping the  needle with a lightly oiled cloth after use to remove residual body salts.