Los Arenales- only had a few days here but lots of climbing to do. I stayed down fairly low below the border crossing/guards house and did a few easy rambling climbs. All the longer/better climbs are up higher I beleive. I was there in November 04 was freezing with lots of snow. From memory it is over 3,500m. Access was a bit difficult. Got a taxi 3/4 of the way then walked last 5km or so. Need to take everthing in with you.
Frey - I couldn't get a guide book in Barilcohe for Frey in 2008. They have one at the refugio. I found an old in the garage recently from an earlier trip. If I can find it happy to scan and email. Again will be on the cold side probably with some snow. Access is easy- bus to town nearby then walk via two different routes. Refugio is great for food/beer at end of day.
Cochamo- awesome climbing and location but lots of rain. Was there in February for 3 weeks and had lots of rain. Not sure what November is like. Good website is http://www.cochamo.com/. Good refugio run by Daniel/Sylvina with very, very limited beer/bread available.
If I was over there again I would go to Frey as there are lots of moderate routes (18-low 20s), routes are easy to access, can stay in refugio and buy food/beer from refugio and easier access. Cochamo had very limited moderate routes, more difficult to get to routes, and generally more routes generally more serious than Frey routes. Los Arenales- bit more serious that Frey, more difficult access, need to take everything in.