Prefer the heart crystal myself. I think it looks cooler...but honestly speaking, I like both because with either one, if I carry it, no one is going to know who it is protecting me haha unless I run into a Tibetan of course
Having said that, I still think the best protection from obstacles is a belief in karma. For example, Dorje Shugden didnt have the karma to be killed because hes a Buddha, and Buddhas dont have karma or suffer from karma... so the Mindroling Lamas couldnt kill him with thier pujas.
So conclusion? If you live your life by the rules of karma, your life will be less rubbish in general. Just saying.
Btw WB, that kind of reminds me - maybe the chakra is the speech aspect of his energy, because it contains written mantras inside? And the crystal is the mind aspect? But Im pulling that one out of thin air, I have no basis to say that!!