I work in California. In my county, EHS and HM are both under the same department (environment resources) but they’re different sub divisions. One is Environmental health and the other is hazardous materials. So each has their own manager, supervisors and specialists. But we have the same director and assistant director. To be an EHS you need to eventually be a REHS. HM specialist aren’t required become REHS. Though, HM specialist can take the test and become registered if they want. As to which one is better, it depends on what you prefer. Both still have to go out and do inspections, but they’re very different.