[jbee]

i think it depends on the agency. in my town there are three in addition to the county. the county pays the agencies, who pay you. you get more if you go through an agency, but our particular one i think has more training in the beginning and yearly required. we get the best pay in the area but our agency usually gets hard to place kids..older ones, behavior issues, etc. it is very rare for someone in ours to get a baby or toddler, or young child without big problems. we got our son because we took his mom too.
i think an agency is supposed to give you more support, and be the go between between the county and you. an agency can get kids from neighboring counties (ours does) where the county gets county kids only, i think.
i think how soon you get a kid depends on the county, if your agency is on good terms with the county, and how much your agency pays. if the county can give the kids to a lower paying agency they usually will. why pay more?
this is our experience, i dunno about anyone else.