Since you haven't ridden a bike in years, I'd say go with a flip-flop hub. Start on the freewheel side and get used to the gearing and handling. Once you feel comfortable, just flip it yourself, only takes a few minutes and a 15mm wrench. Even if you find yourself mostly riding fixed, it will be nice to have the option of flipping to free (with a smaller gearing) if you do a hilly ride.