As an assembler programmer I actually prefer the kempston one, not that it matters much. Never thought about the BASIC angle. That makes a lot of sense.

As far as I recall, the “cursor” joystick interface overlaps a bit with the “sinclair” one, making the two incompatible.

But then again, sinclair had to make the actual joysticks electrically incompatible by switching the order of the wires on purpose, so compatibility was never really a thing back then..