I have been using the Diablo now for 2 months. No flex, no sliping, no problems.
My headset of choice is a Hope Enduro. the only prob is you need to find a dealer across the pond to sell ya one. They do not sell them in the States. SS races, aluminum shell and needle barings all the way around. Also alot of seals to help keep the nasties out. I have beating mine now for 3 months and it never works lose and because of all the seals I can ride during rain storms and water never gets inside.
If you do not want the hassel of finding one I would say either the ChrisKing or FSA PigPro DH.