In my opinion Mountain Lion is the best since Leopard for 5 reasons: 1. New USABLE features like power-nap, airplay, GameCenter, dictation, and more. 2. Not a lot of bugs that affect my use. ( I just started getting into Macs when Leopard was a few weeks into release so initial bugs in Leopard i'm not familiar with). 3. The price at 19.99 is really great. 4. The new Safari is great and very quick. 5. Snow Leopard and Lion did not make as many leaps overall. Especially SL. What do you think?