The BEST Headset
The finest, greatest performing headset that I have ever owned is also one of the best values, the Cane Creek S-3. Commonly available for around $30.
Why not a Chris King headset?
Back in the day of threaded steerers, only two real performance options existed for bicycles, the Campagnolo Record Headset or the Cris King Headset. Both were fantastic options for both on and off road.
Then came threadless steerers and new developements. Chris King was first to the punch and arguably holds a patent on the design, but slowly the others followed and improved their designs. For many years, the King Threadless headset was the only quality choice available, but recently things have changed.
The real Achiles Heal of the Chris King design is the way that the top plate is held concentric to the steerer tube. An o-ring is used to hold the top plate centered. The problem with this design is that when strong enough forces are introduced to the fork, the o-ring gives a little and the steerer is pushed off center of the headset. Many people will see wear marks on their aluminium steerers and a wear pattern on the taper of the base and top plate.
One possible argument for this is that the o-ring acts almost like a shock absorber for the bearings, transfering wear to more cheaply replaced parts. I don't buy it thought.
Keep in mind that I have a lot of respect for what King has done for cycleing and the quality and products that he has brought to market. I just wish that the design for the headset gets fixed.