Gunslingers seem to be the most disliked here and I completely agree. I'm an old-school GM and don't really like firearms in a fantasy setting (unless I'm running a Freeport/Pirate style game, in which case the rules for guns are still broken but acceptable.
But the classes I believe should not be PFS legal are any out of the Advanced Class Guide. We have been playtesting those classes for a while now and I have to say they are all broken or way overpowered. While the concept of hybrid-style classes was a great idea, some don't work the way you might think. I know i'm gonna catch flak for this opinion but thats what my table has experienced.