CHIME Fall Forum would be my choice.
The CHIME Fall Forum is missing from your list of available annual / bi-annual forums or conferences.
You omitted CES, the Consumer Electronics Show, which has been growing fast in digital health since introducing the vertical 12 years ago. As health care is moving into the home and "new entrants" growing the health care and data ecosystem, that would be my go-to if limited to "one." JSK
HLTH is more relevant going forward because it is not as hospital and physician IT centric as HIMSS. It focuses on the innovations in digital health and a focus on preventative health and wellness and not just the sickness and treatment paradigm.