For myself: short hair, like maybe almost like an army cut but with the front and upper part not that short
For others: i dont really care about boys' haircut lol. For the girls tho, if she has thin strands of hair, i think long is the best. If she has thick hair, is it curly or straight or wavy? If it's straight, it can go either way. If it's wavy or curly maybe rather medium or short. I've seen a girl with thick wavy long hair and...its just too thick and too long, but once she cut her hair short at neck length, it becomes absolutely amazing