I would have to say LENGTH~
Although my texture is not the easiest to manage, I know from viewing the simple regimens of long haired natural ladies w/ similar textures to mine (Sonce aka Kemi21 aka Aijo; Sera252, etc,etc) that it gets easier!
But honestly if I were asked this question before I found the albums of successfully long-haired 4B naturals, I would have without a doubt voted for TEXTURE, specifically in the 3C-4A range LOL!!