Sadly, the correct answer is, unless the game is MAC exclusive it shouldn't be mentioned here, so Dues ex, Monkey island, etc are all better on PC .
IF a game is available Mac and PC, the PC version seems to always be superior (even when written properly, such as Starcraft 2, or World Of Warcraft, the Mac version runs noticeably slower than the Windows 7 Bootcamped version on the same hardware) probably down to better vendor and OS support for Graphics drivers ETC, and coders focus on learning Direct X under windows.
And don't get me started on the "Wrappered" games like Dragon Age Origins, i wasted money on that P.O.S Mac port and ended up having to buy it again for windows when i found out the addons support was broken and it ran like a DOG under OSX.
I am hoping the MAC appstore will not allow "wrappered" games, to encourage native porting so that hopefully we will get a good native game.