Most suitable Mac OS 10.6 through 10.9 for early 2009 iMac I have an early 2009 iMac (9,1), currently running Mac OS 10.5. Now I want to use it as a media center and install XBMC, which only supports Mac OS 10.6 and upwards. The question arises, which OS version is the one that gets the best performance out of my system.

It is a 24' iMac with a 2.93GHz Core 2 Duo processor and 4 GB of RAM.

Which OS between Snow Leopard and Mavericks will be the smoothest on my system? Has there been some comparison of the performance with different OSs?
I would suggest to use Mac OS X 10.6.

For my iMac 24" I have tested all newer versions (on different volumes), and 10.6 is running as it should be. 10.9 seems to be okay, but sometimes I see the "ball" and it takes more time until I can go on...

But it depends what you want to do and what you like - newer systems offers new features (and for me this is exactly why I stay on 10.6). AutoSave and recent application (documents) after computer (re)start might be keywords...

By the way: I would recommend to install LittleSnitch. This tool enhances the firewall for outgoing messages.