i wish i was one of those people that wear their hair down all the time, and it still grows. i'm not. so i chose protective styles. even if i do everything else listed but don't wear protective styles, i don't retain length.
I voted for low manipulation styles, because they have helped me retain length.
However, I actually give the most credit to adopting a healthy diet and getting regular exercise. There is a noticeable decline in my hair's health when I slack on these two things, regardless of what I'm doing to my hair externally.
I voted for daily moisture (which to me also includes any DCs or Steam Treatments that might get done).
As much as I know that protective styling can help with retention, I know that if I were to just protective style and not moisturize my own hair underneath, when I take out the braids/wig/weave/whatever then my hair will not have prospered. (yea... it's happened before. Took those twists out and it was dry as a a dang desert and snap snap snap! went my ends). So I really do give moisture the credit.
It is really hard for me to ONLY say daily moisture. Protective styles and oil rinsing have also played a huge role in this as well!! I'm actually retaining my length , and my hair isn't breaking anymore.