If you’re looking for unpredictability, check out the new Path of Wild Magic subclass. I enjoy playing the Berserker subclass, but the best feature about this class, Frenzy, is sort of a double-edged sword, so I wouldn’t necessarily recommend it. The best subclasses for a Barbarian are Ancestral Guardian, Storm Herald and Totem Warrior. If you want to play a class that will almost never die and can deal a crap ton of damage, then the Barbarian is your best bet. The Barbarian is a badass warrior that quite literally rages into battle.
I like the Alchemist the most because I get to live my dream of brewing random wild elixirs and acting like a straight-up kook 100% of the time. The best subclasses for an Artificer are Alchemist and Battle Smith. They’re essentially the mad scientists of D&D and have the power of steampunk on their side. They’re tinkerers of sorts, using everyday objects as a catalyst for their magic.
The Artificer is one of the newest classes from the Eberron: Rising from the Last War sourcebook.