My personal opinion is similar to Nahuel -- I loved the Lakes District but it's similar to many other mountain areas of the world, e.g., the Alps, the Rockies, etc. Southern Patagonia and Tierra del Fuego were truly unique.
A good relaxed month for me would be:
.5 week in Buenos Aires
1 week in/around Ushuaia
1 week in/around Torres del Paine
.5 week in El Calafate
1 week in/around El Chalten
Fly from BA to Ushuaia, bus the rest of the way -- fly back from El Calafate to BA or take the bus (Argentine overnight buses are a great experience in themselves!).
If I recall, the bus ride from Ushuaia-Puerto Natales was 14 hours, then 6 hours to El Calafate, then another 5 hours to El Chalten. Can't recall the price, this was 5 years ago.

