My preference leans either towards core only classes or non-core only. The game I'm playing in has mostly core classes. Cleric, Sorcerer, Fighter, Bard plus we have a couple players using stuff from the APG a summoner and Rogue/Alchemist (we have a pretty large group). As a player and GM I prefer more restrictions because it allows me to focus some character choices. Being told, any PF book and most 3rd party stuff makes my brain melt. Too many options.
Core only lets everyone keep default assumptions, once you add psionics, advanced classes, 3rd party stuff, it becomes a vichyssoise of options that makes the world seem very patchwork. Non-core would be cool since it allows for some really interesting group combinations and makes the players think about the world differently.
What I would really like to see is a thematic restriction, for example an Orc campaign. Races: Orc, Hobgoblin, Goblin. Classes: Barbarian, Fighter, Rogue, Ranger, Druid, and maybe Sorcerer. Possibly add Cleric since my group doesn't like the PF math of encounters being a 20% of resources thing, so the fights are epic but the PCs get really beat up. In a different group I would only allow a cleric if they asked for it.