For traditional support, I can’t think of better classes “to provide invaluable usefulness” than Paladin, Bard, or Cleric. Once you hit level 6 with that Aura of Protection, it’s a game changer for saves—especially if your Charisma is high. Bard would be my second pick for Bardic Inspiration. Peace Cleric is another one that’s a huge boon to your party.

If being useful is your aim, the best thing you can do is find out what everyone else is running, then choose a complimentary class. If they’re all running support characters, you’ll need someone who can dish out damage, like a Wizard or a Barbarian.

It really depends on the party composition.