A note of thanks to Rod Klukas - who read this, and contacted me immediately about the D4 - to send it back to the mothership in France for service. Impressive.
Three different answers - over the past years:
RRS BH40 ball head easy to use, but small droop while tightening. Largely retired.
Linhof 3D leveling is very good, not quite as flexible as the Cube (no 90º, 10º max angle) nicely geared and very stable. Use for long shots or for max stability is needed. .
Arca D4 is the daily standard - quick and easy, works well. A bit tall and heavy. Has developed a little looseness, needs a bit of attention.