Hard to answer for me. I always dated and in the end also married women with hair between hip lenght and mid thigh lenght, but...

Lenght is not Always good. Some women are just hotter with shorter hair and my wifes sister for example rocks with a shoulder lenght styled side parted bob with great volume. She tried to grow it longer and it looked think and sad she said... ^^

Important to me is also, that the hair wont get thin. I prefer if a lady looses a few inches if it makes the ends look thick and healthy as well. To me it is a big turn of if the hair is very long but starts to look like sparse lint in the last half or last third...