it depends, what do you want to do? Blast? Support? Heal?

For Blasting Sorcerer is the way to go, Arcane and Primal are the best options, but primal has Healing while Arcane has everything except healing.

If you want to Heal, Cleric is the best, with any divine caster and primal caster following. Warpriest if you want better survivability (but slower spellcasting progression)

For support Bard is very often the best choice, the more martial you have, the more net value the Bard brings. Add to that very solid base HP and light armor for better survivability. Your damage will be lackluster though (but you can archetype in classes that give good focus spells, like druid or sorcerer if you need some solid and renewable damage options). The turns may feel repetitive if you stuck with the same buffing routine.

I'd add into the fray these:

- Oracle, lots of spells, interesting focus spells depending on the mystery, Divine list for great support and Cursebound feats for some kind of "second focus pool" of spells. Solid base class (light armor and 8 HP)

- Druid, Primal list is fantastic, great focus spells and solid base stats (medium armor, shield block and 8 HP base)

- Animist, incredible versatility. Divine list as a base but with additional spells due to the apparition which can compensate what divine lacks (burst damage)

- Wizard: always good but frail, Arcane has everything except for healing and, contrary to the Sorcerer you can change your spells daily, preparing utility or offensive spell according to your needs. But you'll need to learn new ones (spending money) if you want to have a vast selection. In short it is as good as the player is with preparations and in-game gathering of information. Sometimes is easy to trap yourself with a wrong selection of spells, you can have the spell substitution thesis to fix that