Gameplay-wise, I couldn't really say. I play the game on story difficulty, cause I'm not here for the RPG mechanics XDGuys, I'm new to the game and I'm planning to be a white mage that acts like a paladin. What companions do you think I should use?
Role Play-wise, I'd recommend Brint/Brienne, Azzyran, Etheryn and Atugia. They're the companions with some of the biggest "We're the good guys and we're here to help" energy to them. Cait and Quin could also potentially work, but the way they act is more controversial here. Cait's a friendly white mage who wants to help everyone, but is as promiscuous as the Player, which a lot of people here hate. Quin's a reformed cultist with a questline where you help him become a knight, but he's disliked for being a horndog who doesn't bottom for anyone outside of rare defeat scenes. If you don't mind those character qualities, you might enjoy having them around.
I believe (don't quote me on this) that the companions who have the most flavor-text when travelling/questing are Brint/Brienne, Cait, Etheryn, and Arona.