what is a stable SEP 12 version?

I have been using 11.0.5 for about 2 years now and it has been very stable for me. I am looking to upgrade to SEP 12 and would like to know what the most stable version is according to this community.

I have about 600 desktops and 200 servers in my environment. They are all behind a proxy server that does a very good job of blocking majority of the malicious websites out there. In my current deployment, I use SEP AV + Truscan. I am looking to do something similar with the latest SEP upgrade. In SEP12, I am planning on using AV + SONAR only. I see that the most recent version is 12.1.2. Is this what I should be going to?

Thanks in advance.