I have no idea, what do you like? Dervish is a primarily a melee attacker while Ritualist is primarily a support character but can also have direct spell attacks.
Here is the answer you will see on every "which character is better?" question:
It depends on how you like to play.
Dervish is a melee fighter while the Ritualist is a caster, often used as support. Look into the campfire posts to read more about how to play each type and determine which sounds more enjoyable to you.