I concur with the above. Work on a truck if you want to experience the wider spectrum of emergencies, out in the field. Work in an ED if you want to see from the inside how a department functions.
Advantages (for me) of being in the ED include the experience with blood draws and EKGs, plus many other little things that might or might not come up if I were working on the truck (which would be alongside a Paramedic, in my location). I've held traction during conscious sedation/ fracture reductions; I've held any number of little kids still for IV sticks; I've assisted with casting and splinting; I've dressed wounds. And yes, there are advantages to knowing and working with, say, the EMS director for our county, the director of med student training, the directors of research projects...
One disadvantages of being in the ED is that I'm never the first person to lay eyes on a patient, and I don't do much real assessment. (I've worked at Triage and been the one to decide that a patient needed to be a critical case, but then there were two RNs there who would have done it 0.003 seconds later if I hadn't.) Another is that honestly, the way the job function is structured where I work, you don't need to be an EMT to do it well. There are plenty of us, and some Paramedics too, but your regular ol' Certified Nursing Assistant can do perfectly good work.
Which might mean, depending on conditions where you'll be, that a shorter nursing assistant course could be enough to get you that ED tech job. I wouldn't trade my EMT for anything; I like having scratched the surface of medicine. But it's an option...