I vote for Bariloche for a first timer (ahhh, high school memories!):
For six days:
Rent a jeep and do:
1 day or 2 the Seven Lakes Circuit: rent a car, pass through Villa La Angostura, and sleep in Villa Traful (or not),continue to Valle Encantado, back to Bariloche.
1 day: Cerro Tronador and Cascada Los Alerces, depending on the lack of snow mabye you can see the Cerro Catedral from below on the circuit instead of taking the route behing Bariloche.
1 day: Circuito Chico, do one or two walks on it if you have the energy
1 day: boat to the Arrayanes forest and maybe Isla Victoria.
1 day: relax in the city, go to a chocolate factory, drink hot chocolate, eat deer or another local delicacy, have an ice-cream. Maybe a spiked coffe on the top of cerro Otto? (overlooking all Bariloche and the lake)
And... plan your next trip to Patagonia!, so many places to see.