I have a 24" 2008 iMac with 4gb ram and 3.06 C2D processor. Mine is still running Leopard. I have no interest in investing in any hardware upgrades. However, I am running into a lot issues where software cannot be updated due the OS no longer being supported. I also cannot install drivers for any of my printers due to this. The iMac itself runs without issue. I primary use this computer for guests so they can check their email or do some basic internet surfing. Which OS would be the best to upgrade to? While it does not have to the fastest, I don't want to end up with a machine that is too slow to be usable. I realize there are many such questions already like this one but most seem to involve people who have upgraded their hardware.