The BIG/big method gives the shortest possible chain, but it isn't always optimal for shifting, IME. I prefer the Shimano method, especially for GT cage derailleurs. To do this, when you put the chain into BIG/small (highest gear), the jockey wheels of the rear derailleur should be in a vertical line. Always double check both BIG/big and SMALL/small to make sure the chain is long enough, and not so long that it can rattle against itself. (the latter state can be fudged if necessary with triples.)
I'd take a wild guess and say that 'A' is closest to this method.