I was an EMT for 10 years. I was also a 911 dispatcher. Both jobs have the good and the bad, but neither are jobs where there is any room for advancement and are relatively low paying.
Cops or Fireman = High Pay, Great Hours, Room for advancement
EMT = Low pay, crappy hours, no where to go without changing fields (becoming a medic, doctor, nurse, or a PA)
Also, being an EMT does not give you the respect that fireman or policemen get. They have the lowest budgets and get the least thanks even though they are dealing with life and death more than police or fire. People think of EMT's as "ambulance drivers" with no skill other than pick up the sick and drive them to the hospital like glorified taxi drivers.