Sippy cup! Even though I used juice box more than sippy cup when I was little, sippy cups just pushes me right into little space and it makes me feel relaxed. In case of juice box, it takes a lot of time to slip in little space plus being the clumsy person I am, I tend to squeeze the juice box harder unintentionally and end up soiling my clothes
For me, I think more juicebox works. I'm kinda sorta more in middle headspace, and sippy cups feels more like little. I have regressed to little a few times, but I kinda need to feel really secure and safe to do that.