PG9 and upwards all provide a sort of HA with replication available. I would recommend the latest 9.2 (9.2.8 I believe) or the latest 9.3 (if you need the 9.3 features). One advantage of 9.2 is that it's a little older and a little more tried-and-true, BUT THAT IS JUST MY OPINION (before I get flamed). Cascading replication works very nicely. In any event, you will likely want to do the pg_dump/restore dance on a new system with a new cluster rather than an in-place upgrade.
The replication stuff is well-documented and pretty simple.
If you have further questions, either let us know your specifics here, or email me directly, and I would be happy to advise. I danced this dance over 50 times in testing for our 8x -> 9x upgrade and another 20 or so for my SSD migration.
-------- Original message --------
From: ALEXANDER JOSE
Date:04/03/2014 8:28 PM (GMT-06:00)
To: postgres admin
Subject: [ADMIN] Migration Postgresql
I would like to help and I'm going to migrate postgresql version 9.0.4 to a higher, 9.3, which is the most stable?
High availability to place 2 postgresql servers, which would be the best settings to provide active active nodes.
alexander
DBA Postgresql
Venezuela