Classes are ranked by dungeon farming speed, boss damage, gear dependency, survivability and overall endgame viability. This list is updated after every major balance patch.
Elemental Mage is currently the strongest class for overall progression and dungeon farming. Its massive AoE damage lets you clear entire screens of enemies faster than any other class, making it the fastest way to farm gear and level up.
Paladin is the most beginner-friendly class thanks to its high survivability and simple playstyle. If you prefer dealing damage, Rogue is straightforward and strong even with average gear.
You can respec your skill points, but your base class selection is permanent. It is recommended to plan your build ahead of time to avoid wasting resources.