Here is the standard breakdown used for normal ops at ATL
South Vectors (SOONE, SOTWO) and East Vectors (EAONE, EATWO) use 9L
/27R. This includes all traffic bound for the northeast and Europe.
North Vectors (NOONE, NOTWO) and West Vectors (WEONE, WETWO) use 8R/26L. This includes all traffic for the midwest and west coast.
Arrivals from the northeast (MACEY) and northwest (RMG) are vectored to 8L
Arrivals from the southeast (SINCA) and southwest (LGC) are vectored to 9R
Note: This is the standard breakdown. At certain points in the day (i.e. the 2000z hour), the arrival rate jumps to 120+. If 80 of those are inbound from the northwest and northeast, they may very well get vectors to the south runway, and vice versa.