Some very respected turntable manufacturers like Basis and Sota do not even give you a choice. Many very smart engineers look at 12 inch arms as being foolish.
Although Basis does offer its TOL SuperArm as 12.5" and 16". And Origin Live, while acknowledging the downsides of longer arms, still says it prefers the 12-in sound of its arms. So sonic preferences, the final arbiter, do play a part.
OTOH, Bob Graham famously said the 9-in arm was his best sounding, and many people say the 9-in is the best sounding 4Point.
I’m about the install a 12-in Phantom on the same turntable as a 9-in for the first time, which should make for an interesting comparison.