I once owned an AE-II, and later purchased an AE-III. Within the fundamental limitations of using any reflected light meter, the AE-II and the AE-III are perfectly accurate meters! I shot many weddings professionally with both meter prisms, as well as shot many color transparencies (and we know that has very little lattitude for exposure error!) using those meters.
The AE-II and AE-III are equally accurate; the AE-III is more precise (1/12EV metering precision with 1/6EV exposure control for AE-III, 1/6EV metering precision with 1/3EV exposure control for AE-II.
I know the AE-II and AE-III meters were accurate, because I had test standard of Minolta Spotmeter F and Minolta Autometer IVf to compare readings of gray cards against.
The mechanical fit of any of the Bronica prisms is a bit loose even when both camera and prism are new, but I have never found the looseness to have any affect on connections between body and metering prism and the resulting accuracy.