Alpharetta and Roswell are too far out to not have dependable vehicles plus there aren't many options for either. Sandy Springs is on a bus line and near a Marta Station that can route you to anywhere within the city. The schools are good in Sandy Springs. It's a good area!
http://www.trulia.com (Rentals Section)
http://www.zillow.com (Rentals Section)
http://www.realtor.com (Rentals Section)
Between all of those, you will get a very clear picture if you can find what you are looking for. Good luck!