I recommend FSA DH Pros.
If you're looking for a threadless headset which is
- solid,
- smooth,
- strong,
- easy to install,
- easy to maintain,
... then you should invest into one.
I have experience with them and after you wear them in, they are sooo good. Sealed bearings are also 50x more durable because we all know that unsealed headset's cages can snap/bend/break or you can just loose your balls when maintaining it.
After you buy it, you'd never want to ride unsealed headsets again.