I lived in Argentina for four months and spent one month of it driving through and camping in Patagonia. It was an amazing trip. The scenery was incredible. The people were friendly. And I highly recommend it. I wrote about it on my blog but I'm listing the highlights below. I'll be traveling again from November 08-May 09 and I want to do another long drive, maybe for the entire period. I'm thinking about either staying in the U.S. for the drive or going back to somewhere in South America so I'm joining Roadtrip America to try to figure all that out.
map of the Patagonia drive. You can see I made a big loop, but I did the stretch from Buenos Aires to San Martin de los Andes by bus, then I rented a car in San Martin. I took an entire month for the loop but that's because I stopped and worked some as well.
The best parts of the drive were: the 7 lakes district, Cablo Blanco at low tide, Peninsula Valdes (although not as great as Cabo Blanco), Copahue, the steppe - I drove too much of this. By the end of my trip, I was really tired of nothingness and I'm a huge fan of nothingness (I love middle of nowhere Arizona, for example). But, I think you have to experience it some...at least for 8 hours. But, I do admit that there was a lot...a lot ... a lot of nothigness. Just one of my posts on it: there are many such posts.
Puerto Deseado - I really liked this place, but really it's just a small somewhat run down fishing town. It feels very real to me, though.
I rented a car from "Easy Car Rental" in San Martin. It was fantastic and I wrote about it here: Warning: Almost all cars in Argentina are manuals. Even if you won't be leaving from San Martin, the owner of Easy Car Rental, Jorge, was really awesome and he had worked in several companies before starting his own - he could probably give you a recommendation for whatever city you choose to rent from.