Amazon's medical coverage is no UPS but it is extremely competitive against plans that union members try to tout as better. See https://news.ycombinator.com/item?id=26753455 as an old discussion where the thread creator thinks their plan is a lot better "due to unions" but it's actually a lot worse.
Work a union job, not Amazon?
UPS benefits will easily cover your medical and dental problems. (Once you qualify.) I don't know anything about Amazon's worker coverage.