Quick answer
Both are expensive, top-schooled Fulton County suburbs with a 7.75% sales tax and no MARTA rail. Alpharetta is the more walkable and amenity-rich of the two, with Avalon, a rebuilt downtown, and a dense tech-job base. Johns Creek is slightly more affluent and residential — known for gated golf communities and some of the state's highest-ranked schools, but with fewer walkable centers. Choose Alpharetta for lifestyle and walkability; Johns Creek for large-home, top-schools suburban living.