I have a Ninja Blender and the NutriBullet Pro. I love them both, but I use my NutriBullet a lot more because it has more of a "make-and-go" capability. I drink on the way to work, then clean it out once I'm there, vs. having to clean out my Ninja before I leave and then clean another cup. I also prep my smoothies the night before in the cup and stick it in the fridge with the lid, then spin the blade on in the morning. (I sound like their infomercial!)
I think it all depends on what you want to use it for/how many people.