Which version of OS X should install on a 2006 MacBook?
Depending on what MacBook version you have, you may be able to install different OSes.
However, what I do recommend is the best, and most stable OS that Apple has yet to ship: Snow Leopard, which is 10.6.X as you say. 
You should do a fresh install – not from a iMac CD, but from an retail Snow Leopard disc!
All apps but few still support Snow Leopard.