It's utter nonsense to claim one is adier than the other.
DD couldn't be put down til she was about 3 months old - she'd be happy as anything in my or anyone's arms but scream til she was purple if put down, so I didn't sleep much for 3 months. Then she gradually improved, but was quite high maintenance throughout her babyhood.
Ds1 was an angelic, perfect baby who slept 4 hours, fed well, slept another 4, never cried without a reason which could be easily sorted really.
So boys are easier. Waaay easier. Piece of cake compared to girls.
But
Then I had DC3 who almost broke me...
A boy...
So second babies are easier?
Or third ones are harder than first and second put together?
Or the first boy is the easiest baby?
Or autumn babies are easiest...
Or perhaps it depends which way the wind was blowing when they were born?
It's all bollocks, you can't know based on genitals or birth order how easy your baby will be.