If you're doing it with extensions, I prefer braids. They hold much better and your hair stays stretched straight so that when you undo, you aren't dealing with strands that are curling around each other (if you're 4B especially).
If you're doing it just with your hair, I prefer twists because braids on my 4B hair left in for long w/o extension hair to keep the strands apart, start to lock up. I think extension hair helps to keep my strands in each of the 3 section apart so that it's easy to undo with my fingers.
I don't think I've ever left twists in for 3 months. I am always feeling my hair looking for twists to do. The only record I have for certain is the twists I left in for 4 weeks. I'm not sure why I kept track then. I usually don't pay attention to how much time is lapsing but I do know I am always playing in my hair and once I start redoing one twist, I go to another...and in the course of the week I've redone all and cannot wait for them to get messy again so I can play in my hair.
As far as being protective styles, they do fall short unless you will wear your ends hidden in clever updos. But if you'll leave your hair hanging down, then the style isn't really a protective style but more a low manipulation style.