In today's climate, which ever system that can gaurantee us no more cuts is the one for me. If I have to provide EMS from my Firehouse to stay employeed, so be it.
As read from the above replies, almost all answers were based on the need and size of the AOR. I'm from a different country but i do agree on some points. Here, we have a 3 tier, the FF, the rescue and the EMS. We are under an umbrella agency called DILG (Dept of the Interior and Local Gov'ts) that's why most units are being supported by the respective localities... volunteer FF are separated from the paid FF.
Whenever there is an alarm, volunteer FF and paid ones respond. Rescue teams will only respond upon verification of the need for their presence. The EMS responds to all medical emergencies and non-emergencies. The 3 units responds altogether when there is a major incident like bombing, plane crash. structural collapse, vehicular alarm with multiple casualties and other major incidents requiring extrication and emergency medical interventions. The EMS is the unit that has a highest alarm rate, we get an average of 3 alarms a day.... the worst was when we had 11 alarms (27 px) on a shift (24 hrs).
The difference of our organization from yours is we lack advance equipments and facilities that is why we have to double our efforts which puts our men and women to more risks. In a 3rd world country like ours, in spite of our lack of training on some areas and the out- dated equipments and gears, our umbrella organization and the bureau saw it fit that we have a 3 tier. Mixing EMS and FF will not be effective here. Coordinated efforts are observed only when needed.
I prefer combined, but then again here in Chicagoland all we have is combined Fire/EMS, so I guess I'm a little biased as far as what I prefer. Stay safe!