Re: Which circuit to choose?
Ideally it would be best to run a new circuit from the panel to supply the fans and possibly another receptacle.
Barring that , I would personally choose the second choice of tying into the less frequent used receptacles from the basement. Less chance of overloading the circuit as well as reducing any chance of *noise* being introduced into the circuit for more critical items like your audio / video equipment , from the fan motors.
"" an ounce of perception -- a pound of obscure "