I do both, I'm a Fire Medic. It depends on the call, sometimes fire, sometimes medical? Over all, I Think its pretty close. Maybe being a paramedic might be a little more stressful, because you can make a choice of treatment or not treat in time. Your always dealing with a Pt on medical calls, not all the time on fire calls. Things could get bad pretty fast on medical and trauma calls. Dealing with family members, children, things like that. Runnin a call on children, always makes your butt pucker as a medic, I don't care how long you've been doing it.
I agree with you KIT. There really isn't anything more frightening than having a patient loaded into the ambulance breathing and before you get to the EC, they are not breathing. Makes for a tense fifteen minutes!
I work as a FF/Paramedic and both can be stressful at times. We do however respond to more medicals then fire calls. On a rare occasion we have more fire calls and I laugh with the crew and say "Hey, we are like real firefighters today!"