Hello

I am going to be visiting my son for 10 days in valparaiso chile in February and he suggested to take a 4 day trip either to patagonia or san pedro de atacama.

They both seem beautiful. I was in Wyoming, Colorado and the Canadian rockies and it looks like Patagonia.

Is there anyone that has been to both and give a suggestion?

Where is more to do ?

What is better to rent a car to get there or fly a plane- I know that they are very far from Valparaiso or Santiago

4 spent 5 nights in patagonia. the glaciers are stupendous. perito moreno is the only advancing glacier in the world. although many visitors to the glavier lands base themselves in el calafate we were also able to spend time in the much small chaltan as wellw/ awesome hiking and more glaciers

cheers
AndrewDavid

If you were going to spend 4 days in Patagonia, you would need to stick to Chilean Patagonia. You don't have time for El Calafate, which is in Argentina.
February is high season in Chile and the most difficult time to find transport and lodging to popular spots like San Pedro and Patagonia. The logistics for San Pedro are somewhat easier, so I would look at flights to Calama first. You can book a shuttle from the airport to San Pedro.
http://www.sanpedroatacama.com/ingles/home.htm
Another option would be to fly to Balmaceda and visit the area around Coyhaique on the Carretera Austral (southern highway). This is a very beautiful area and less crowded in summer.
http://www.interpatagonia.com/coihaique/index_i.html

I went to both, one right after the other, in 2008. For you, I would recommend Patagonia (e.g. Torres Del Paine) over San Pedro. This isn't because Patagonia is "better" in any regard, but because the Altiplanic Winter in the Andes is January-March. While San Pedro itself would probably still be dry, the nearby areas in the Altiplano, such as the Tatio Geysers, would be at risk of snow, flash floods, etc. So for February, I would recommend Patagonia.

The area around San Pedro does not get flash floods or any other kind. The Altiplano winter does not affect it. It remains dry all year. If you were travelling into Bolivia it might be an issue, but not around San Pedro.