I found this online list of the game's classes (not including those made by Rune or Neidan masteries), each rated by the difficulty they are to play.

Easy classes:
The Spellbreaker: Dual Melee/Pet (Warfare/Spirit)
The Spellbinder: Melee/Sheild/Pet (Defence/Spirit)
The Champion: Melee/Pets (Warfare/Nature)
The Conqueror: Melee/Shield (Warfare/Defence)
The Guardian: Melee/Shield/Pets (Defence/Nature)
The Warden: Spear/Sheild (Defence/Hunting)
The Ranger: Bow/Pets (Hunting/Nature)
The Diviner: Melee/Sheild/Pets (Dream/Spirit)
The Ritualist: Staff/Melee/Sheild/Pets (Dream/Nature)
The Templar: Melee/Shield (Dream/Defence)
The Conjurer: Staff/Pets (Earth/Spirit)
The Harbinger: Dual Melee (Dream/Warfare)
The Summoner: Staff/Pets (Nature/Earth)
Medium Classes:
The Corsair: Melee/Sheild (Defence/Rogue)
The Juggernaut: Melee/Sheild/Pet (Defence/Earth)
The Elementalist: Staff/Pets (Earth/Storm)
The Avenger: Bow/Pet (Earth/Hunting)
The Oracle: Staff/Pets (Storm/Spirit)
The Druid : Staff/Pets (Nature/Storm)
The Brigand: Bow/Spear/Sheild (Rogue/Hunting)
The Warlock: Staff/Pet (Rogue/Spirit)
The Soothsayer: Staff/Pets (Spirit/Nature)
The Haruspex: Spear/Bow/Pet (Dream/Hunting)
The Evoker: Melee/Pets (Dream/Earth)
The Harder Classes:
The Assassin: Dual Melee/Traps (Warfare/Rogue)
The Slayer: Dual Melee (Warfare/Hunting)
The Thane: Dual Melee/Pet (Warfare/Storm)
The Battlemage: Dual Melee/Pet (Warfare/Earth)
The Paladin: Melee/Sheild/Pet (Defence/Storm)
The Sage : Bow/Spear/Pet (Hunting/Storm)
The Bonecharmer: Bow/Spear/Pet (Hunting/Spirit)
The Magician: Staff/Melee/Pet (Rogue/Earth)
The Illusionist: Staff/Melee/Pets (Rogue/Nature)
The Sorcerer: Staff/Melee/Pet (Rogue/Storm)
The Dreamkiller: Melee/Spear/Sword/Traps (Rogue/Dream)
The Prophet: Melee/Pets (Dream/Storm)

I found it at https://titanquestfans.net/index.php?topic=617.0

Apparently, some classes are easier to play for beginners than others while others are harder. The list, however, does not include any classes made by either Neidan or Rune masteries. So I have no idea of the difficulty those classes are to play. Whoever made this list needs to post an update.

Bear in mind this is a very old list so things might have changed a fair bit with the AE version of the game coming out plus all the expansions since then as well.