The Major players of San Diego EMS are AMR and Rural Metro.
Both are somewhat difficult to get on with if you have no experience.
AMR is responsible for ALS transports in Chula Vista, National City, The San Miguel Fire Protection District, Lemon Grove, La Mesa, Alpine, Jamul and Campo. The east county rural units cover several other areas adjacent to Alpine, Jamul, and Campo.
All 911 units are two paramedics, for a long time the rural units were EMT / Paramedic but within the past year this has changed and AMR San Diego no longer runs any EMT / Paramedic rigs. ALS units work 24 hour kelley schedules.
AMR San Diego BLS spans the entire county as do all BLS services. They are moderately busy, and work 12 hour shifts with alternate 3 and 4 day weeks. AMR Employs CCT-RNs for interfacility transports.
AMR is difficult to get on with, they will tell you straight out to go to one of the smaller ambulance services for experience. The EMT pool in san diego is saturated so getting any kind of EMT job at all right now is pretty difficult, so you have to be persistant everywhere.
Rural Metro runs the ALS for the city of San Diego, they work 12 hour units and run with an EMT driver and a Paramedic. They are probably the most difficult of all the services to get hired on with as they are the highest profile and get the most applications. They employ RNs for interfacility CCT transport.
Metros BLS units work 10 hour shifts and are moderately busy as well.
There is also a company called Mercy Ambulance who have ALS contracts in the rural north east portion of the county, covering places like Valley Center and Palomar Mountain. I Don't know much about Mercy but I think they are EMT / Paramedic with 24 hour shifts.
All other companies listed below are BLS some with CCT and some without.
Care is the next largest ambulance company running a good deal of BLS ambulances and having a partner company Med First which provides CCT-RNs for critical care transport. They are a good company and a lot of EMTs in San Diego get their start there. They run 10 and 12 hour shifts I believe.
Here is a quick list of the small ambulance providers in the county:
Balboa: mostly north county (Tri-City Medical Center is their major contract)
AmeriCare: Have some money, nice rigs 24hr shifts, laptops for charting.
Pacific: Nothing special, a few 24hr shifts but you need a lot of seniority.
AirCare: 24hr shifts, and the opportunity after some time to work on fixed wing interfacility transport flights with an RN.
Alert: Nothing special.
South Bay: 24hr shifts.
Priority One: Nothing Special.
Schafer: Has paramedic contracts in Imperial County, so you could work for them as a medic out there after paramedic school, 24hr shifts.
GreyHound Ambulance: brand new, I don't know if they are running calls yet.
Max Care?: Also brand new, I don't know much about them.
Let me know if you have any other questions about San Diego EMS.