Alchemist: One of my favorite classes. I love the bomb throwing and just the range of different things you can do. Sure, spells can do it better, and often to other people. But I've turned alchemists into everything from front line combatants to woodland hermits to poison crafting and bomb throwing leaders of thieves guilds. Cognatogen is also fun. Instead of a Hyde type, you get a brain-Hyde.
Cavalier: Some people love them. I've always been really so-so about them. The focus around mounted combat irks me. However, I've come to love them with the addition of the Huntmaster archetype.
Gunslinger: While many people are completely anti-gun in their fantasy settings... I love it. As long as you restrict it to early (musket style) firearms only. I've used Gunslinger for a few different roles. I actually did a mix of mysterious stranger/paladin at one point and had a blast with it.
Inquisitor: Another enjoyable one. A bit more slanted towards combat, but it has enough skill potential to turn into a skill monkey. I wish the teamwork feats were just bonus combat feats, but that's really my only complaint about the class.
Magus: I've never played one. I've designed quite a few that I intended to play, but I've never been able to actually play one. I think they look pretty cool. I enjoy using them as villains in my campaigns though.
Oracle: Really a sorcerer version of the cleric, but with added flavor. I think the curses could have used a bit of working, maybe give some bonus a bit earlier than they do. But I do like the class a lot. Half orc metal oracle probably being my favorite. Was a great front-line bruiser.
Summoner: I don't like them. Not for thinking they're overpowered. But just because of their bond with the Eidolon. Being able to see through their eyes, dismiss them instantly. And having no downfall to just treating them like crap... I've seen too many Eidolon's turn into trap finders and little else. Pretty annoying.
Witch: I like it, but I'm honestly done with the Slumber Hex. I'd love to see a single witch that's built without it. Alas, that's yet to happen.