I've heard great thing about the Stronglight A9, and I'm not sure I've used one or worked on one. It has roller bearings, right? That sounds smart. When I was a bike shop mechanic, I noticed that Stronglight headsets in general lasted longer than did Campagnolo headsets, even though it was clear that Campagnolo headsets were ground with much greater precision. Maybe the design or the precision with which it's made, made it more vulnerable to misalignments. We would not install Campagnolo headsets without first machining the head tube and fork crown. Without doing that, we knew the Campagnolo headset would live a short life.

Maybe it was the designs of the curvatures that created the vulnerability, not the precision of the grinding.

I've used a couple of headsets with cartridge bearings, the kind made for threadless forks. I think they are needle bearings inside. I haven't used them heavily yet, but it seems like a smart, durable design, and they're inexpensive.