If you're looking for 4 acres within reasonable driving distance to APG that's affordable and "safe," you're probably going to need to look in the northernmost areas of Harford County. Check a map for Street and Cardiff. These are quite rural areas, though, and I'm not sure I would call them towns. I have a lot of friends who work at APG too and live over the state line in the Delta, PA area too and have nice hunks of land.
Havre de Grace is probably the "quaintest" town in the county. It has a real downtown with shops and decent restaurants and a sense of community.
Bel Air is by no means quaint. It's pretty much sprawling suburbia at this point with traffic to match. It does have a nice downtown area, but not the ambiance of Havre de Grace which has the water going for it.
Here's a link to descriptions of the various schools:
http://www.hcps.org/Schools/Profiles/profiles.asp (broken link)
And here's a link to some test score data. I've summarized the 2006 data below.
http://www.baltimoresun.com/news/loc...-local-utility
The percentage of high school students in the Harford County who passed the Maryland High School Assessments in three core subjects - algebra, biology and government...
Harford County high school test scores 2006
ALGEBRA BIOLOGY GOVERNMENT
Maryland 66.6 67.8 74.2
Harford Co. 72.8 68.7 78.4
Aberdeen 46.8 49.9 62.7
Bel Air 71.8 77.9 90.5
C. Milton Wright 60.9 65.2 85.1
Edgewood 54.6 65.5 62.4
Fallston 73.8 69.9 86.3
Harford Tech 68.9 78.6 92.3
Havre de Grace 70.9 74.8 81.9
Joppatowne 68.3 67.8 69.9
North Harford 61.4 78.9 84.8