SEP 11 to Sep 12

All,

I have SEP 11.0.6100.645 running and managing clients on a Windows Server 2003 server. 

I need to migrate to the latest version, 12.x? 

In addition, I also need to retire the server 2003 and migrate to Server 2012 / Server 2008 R2. 

So, what is my best process here?

Install SEP 12 on a new 08r2 machine and migrate clients?

Upgragade SEP 11, and them move SEP 12 to new hardware?

Complicating things is that most of my clients are in 'user' mode, and I need to get all computers into 'computer' mode. 

Thanks for your suggestions.