When you're employed by someone else, they'll cover their half of FICA taxes (6.2% each), offer health insurance, HSA contributions. It might be possible in Atlanta to secure a compensation package that includes RSUs or access to an ESPP plan.

I'm not sure if you are covering both halves of FICA or not, but the above benefits could explain the difference, e.g., $120k + benefits = $160k.

Financials aside: If you're the type of person that likes switching companies once every 12 to 18 months, contracting could be a good fit. In my personal view, to really master a role, you need to be in it longer than that. It takes a junior engineer a couple years to become mid-level; the same for mid-level, to senior, and so forth.