The warrior is the starting class. His Spinning Slash ability can be powerful when used effectively as part of a high-damage build, but the Warrior tends to be overshadowed by the Rogue's better scaling in the long run.
Rogue is the first unlockable class and can be found starting on Floor 11 of the dungeon. Rogue's ability 'Stab' adds extra, faster attacks for a brief time, effectively granting +400% dps for 1 second. Unlike Warrior, this ability scales well with high attack speeds, making Rogue a solid choice for most journeys into the dungeon.
Mage is a mobile fighter who can teleport around the battlefield dealing extra damage. Unlock the mage by finding him starting on Floor 22 in the dungeon. Mage's teleport deals up to 150% of his dps to enemies and can be used to navigate in and out of combat. When played carefully, the Mage is potentially the most powerful character in Rogue Dungeon, but in practice the Rogue class is more effective in most circumstances.
The monk is a fun and unique class with a low-cooldown special ability called "Flying Kick" which will instantly engage and damage an enemy in range. At level 5 the upgrade "Ricochet" causes Flying Kick to immediately bounce to a new enemy if the first dies, letting the Monk clear dozens of enemies in seconds if he is already strong enough. Flying Kick does an insane 1 second worth of DPS when it lands.
The Monk's unique skillset makes him an exceptional farmer able to clear levels very quickly at earlier difficulties, but he tends to die quickly when pushing new difficulties due to his high-engagement strategy.
If you love the Monk anyways and want to play him even on challenging levels, his alternate Level 5 ability, Exploding Kick will knock enemies away from his target when he lands a Flying Kick. This helps isolate enemies to avoid the Monk getting swarmed.
The hunter is a unique class that can use ranged weapons. This is a very different playstyle than the other classes. From afar the hunter playstyle can be much safer than other classes.