Druids have a 'spells-per-rest' mechanism very similar to Wizards and Priests. Abilities of Ciphers and Chanters can be used every encounter without resting, so you could consider those.
Every party composition is viable but Priests are the only class that have spells against debuffs such as charmed, paralyzed and dominated that some higher-level opponents seem to love and that can make fights really difficult. Another way of dealing with those debuffs would be to create scrolls against them but the character(s) using them would need to have high lore. Something to keep in mind maybe.
