Thanks. Not sure what a paired stall is?
They all have numbers on them - 1a to 6b.
Each pair (1a/1b, 2a/2b etc) shares a supercharger cabinet with a total of 145kW of capacity. The first car to arrive gets as much as it wants. When a second car arrives, it gets only whatever capacity the first car isn't using, except that a minimum of 30kW is given to the second car, and the capacity can only be shared in large chunks.
So, when arriving at a supercharger you ideally pick a stall that isn't already shared with someone else - though if half the stalls are in use then you may not have the option. If you are forced to share and can guess who is likely to leave next, sharing with them is obviously best - obviously you can't easily guess, but if you followed someone else into there, sharing with them is a bad idea.
1A vs 1B doesn't matter in itself - it's whoever got there first out of A and B that gets the lion's share.
At most sites, the stalls run 1A,1B,2A,2B along the side, so people tend to pick the best stalls just avoiding parking next to someone else, but this isn't the case everywhere (a few sites have all the 'A' on one side and all the 'B' on another), so it's best to check the numbers if you care.
Usually the impact of picking a shared stall isn't that bad - you have to be unlucky to pick someone who arrived not long before you, was completely empty, and intends to stay there until fairly full.