With the rewrite, Inquisitors are less 'fiddly'. Their judgements are a flat scaling bonus, but their spells give them the ability to give themselves a round by round increasing bonus as well to a specific quality or bonus type. they make for a very useful 'combat bard' and 'diplomat' without stepping on the bard's toes at all, and they make an excellent choice for fighting alongside a Cavalier or Rogue, as well as backup for Paladins. They also make a very good replacement for a 'combat cleric', which is slightly harder to do since their spells were nerfed.
Witches are also useful. They are essentially debuffers with their Hexes, and their limited spell selection (with many being taken from wizard and druid) makes them a choice for arcane casters who also want to take over for a healer. While they may be dependent on their familairs to get their spells, a witch whose familiar is killed is better off than a wizard who gets his spell books destroyed because they can regain a familiar with more than just a few basic spells and they have their hexes to fall back on. The DC for the hexes isn't any more powerful than that of wizard or clerical spells, because there are no feats that can increase the Dc except for ability focus, a +2 one time only bonus. They also can't quicken or enhance the supernatural abiltiies, only the spell like ones.
And to be perfectly honest, they disproved the "summoner better than fighter" back when summoners were supposed to be broken, before they got their nerfs in the APG. Without the spell like ability to give their eidolons things like Wish, summoners are great for summoning either a small army of minions to deal with non-combat stuff, or using their eidolon and acting as a buffer for the party as well as second rank combat (archery, thrown weapons, etc).
Interestingly, Summoners, , Paladins, Barbarians, Fighters, Druids, Wizards/Sorcerers, and Rangers now all have mounted class options (wizards and sorcs from spells, but still). A cavalry campaign is no easily in the realm of possibility.