I always try to use the latest releases. My Hackintosh is running 10.11.2. I actually forget where I started, but the basic build has been going strong since late 2009, now upgraded to a 6-core Xeon 5650 @ 4+ Ghz, 32GB RAM, native Apple Bluetooth/Wifi card for handoff/continuity, ~10TB storage (SSD + HDD), and yet the same old ATI XFX single-slot 5770 driving a 27" LED ACD. But man, it still tops out around 20K Geekbench... talk about longevity from a computing power standpoint. I won't change platforms until I can get 8 overclockable cores for a reasonable price....
rMB is on 10.11.2
CoreDuo MB is on 10.6.8, since that's the highest OS it supports. But it's long in the tooth. I traded my 12" Powerbook Titanium for this machine nearly a decade ago. The Superdrive has since given up the ghost. The fan has been dying-- loudly, and agonizingly-- for over a year now. Ethernet port is kaput. But it's got 4GB RAM and 240GB SSD-- it's surprisingly able. I wouldn't upgrade, but any minute now the fan is going to give out.. and the lack of being able to update software (chrome!) because of the 32bit EFI, the inability to even load a version of iTunes that will interface with an iOS 9 device (updated via iTunes, mind you!), and the reduction of battery life to approximately 5 minutes... means it's on its last legs.