A makes the most sense in respects to 2 pair voice. (pin 4-5 and 3-6)
B makes the most sense in respect to T1. (pin 4-5 and 1-2)
In both of the above cases whiteblue, and whiteorange are going to be the pairs in use.
Neither a or b make sense for 10/100 Ethernet. As this type of communication uses (a) second and third or (b) third and second pair for RX and TX respectively.
RJ31X and alarm CPE make me go insane.
Regardless of chosen pin out (a or b), ring should always be on the right when working horizontally and tip should always be on the top when working vertically. Pairs should never be split when the option to maintain the pair is possible - Even for short distances.
