This is all *in general* and not a definitive answer, so I don't wanna hear about someone who saw a support ranger rocking an elk cause that's a bit more niche than I believe this question was asking.
Per class:
Ranger: Most people do a horse for the added dex, and it's great for pretty much any build. You could also look at a wolf or tiger if you're going for a skill-heavy build endgame.
Mage: Elk is probably your best bet, but some people like the defense and skill that comes with a wolf.
Druid: Same as Mage. Shoutout to totem builds (who probably use a wolf).
Rogue: Similar to Ranger, but some like to go bear for the extra health as rogues take more hits due to not being at range.
Warrior: Bear is a very solid option especially if you want a tankier build, but you can do tiger, horse, or even wolf if you can build around it.
Hope this is helpful and if I'm not right, I'm sure someone will correct me soon

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