Speaking for myself. Level 1 is basic CoA, invisible or hardening. Level 2 is barrier haki considered as advanced by Luffy (showcased by the boa's sister and Ray and kizaru's nephew). Level 3 is internal destruction which is the advanced version of the barrier haki. The haki beam is a new theory, showcased by Roger against Oden and by Yamato against a number. We don't know yet where it stands on the CoA hierarchy