Although not the ones you ask about, I have owned 4 MF integrated amps, X-A100R, A3, A308, and A5. They will definitely sound more alike than sound different. I still own and use the A308.
I would choose the A300. It is one generation older than the A3.2, however a step up in the line of MF integrated amps. The A3 and A300 were current at the same time. The A3 was replaced by the A3.2, with the A308 replacing the A300. IMHO, the sound of the A300 will be closer to the A308, and sound of the A3.2 will be closer to the A3.