Public health is a weird field. In essence it is mostly a social service and found in the government sector. Government jobs usually have lower salaries than private sector jobs (benefits may be better though). However, the skills learned in many MPH programs, especially epidemiology and biostatistics are easily transferable to many private sector fields, such as managed care or pharmaceutical/clinical research.
Also, while the private sector may pay more initially, some might find it easier to move up the ranks in government (just because of the sheer number of agencies). Rather than focusing specifically on salary, I would look at the type of lifestyle you want.
I've found the biggest difference between the governmental and corporate world to be how to climb the career ladder. Government public health, especially at the local level may require frequent job changes. After my bachelor's degree, I started out as a health educator in a LHD, two years later I worked as a state preparedness analyst, and now I'm a regional preparedness coordinator in a different part of the country. My ladder requires me to move. Though the moves slow as I progress. In this time I've finished a MSc in epidemiology and started a DrPH program. I've also increased my earning by roughly $20,000 in five years.
I also worked in the corporate sector for awhile. Personally it wasn't for me, but starting salaries were higher, but climbing the ladder was reserved for only the best. Others remained analysts for their entire career. This ladder however, would have allowed me to stay in one place.
Just some food for thought.
