I'm right handed so upside down right leg for racer's right side up for my white birds, my son is left handed and bands his upside down left leg! Also I don't band the babies until pin feathers are showing pretty good!
I grew up always putting the bands right side up on the left leg. Idk what it is but I just can't stand a band when it's upside down. It used to be where I'd see a bird in an auction that I liked that had an upside down band and wouldn't buy it. So I stopped looking at the bands. LoL But thats just me I'd rather be able to read the band right side up when the bird is sitting on it's pearch or on the landing board because that's when I learn the birds numbers and by the time the races come I know all thier numbers already.