avionic type,
Myself, I was brought up on the "duplex monitored" principles used on Concorde (and earlier on the VC-10?).
Slightly more hardware, possibly, since each of the two computers contained a complete "duplicate", charged with monitoring the "command" side, and handing over to the other one, if "command" and "monitor" disagreed.
The two computers barely talked to each other (the standby one stayed synchronised, but "kept its mouth shut"), while a triplex system involved a lot more data being exchanged and compared between the computers, hence more and differently designed hardware.
I have no idea what really was the best solution..... espcially since not so soon afterwards we went to digital systems, where we were dealing with a whole new ballpark.
CJ