My family and I are also thinking of moving to Atlanta and would appreciate any suggestions.
I hardly ever go to College Park but from what I hear and what I've seen, it is very transitional with a high rate of crime and poverty. You've cited a broad list of counties that are very diverse - Fulton is predominantly urban and metroplitan, where Paulding and Henry are fairly rural. Perhaps you should visit the area more extensively to determine what suits your needs.
I'd have to agree with JAtlanta. College Park is struggling to become a more inviting area but there's still a lot of work to be done before it gets there. I would be more apt to look in the South Fulton area, where some really nice neighborhoods are being built. College Park is just too iffy, in my opinion.
I would not move to Clayton County. The schools just barely got their cerfication back after being on an advisory status. There's also been a good bit of gang/drug trouble in the last few years. They're starting to build some community centers for the teens but I think it's going to take a while for change to come.
Henry County, which indeed used to be rural, is becoming a big draw. There's a lot of affordable housing out there and the schools are pretty good, too. Worth a look for sure.
Paulding County is also starting to change from being largely rural. Many new subdivisions going in. However, it is WAY out there. If anyone in your household is going to be working downtown or inside the Perimeter, the drive in terms of traffic is going to kill you. I know someone who lives in Paulding and it takes her over and hour just to get to Roswell.