One of the quirks of character creation in Cinderheim is that the land's demonic corruption grants starting character access to two cantrips from any spell list.
As someone on G+ pointed out, not all cantrips are created equal; some are obviously better picks than others, especially when taking Cinderheim's particularities as a setting into consideration. These are the cantrips I think would be most useful in the setting:
If you really want a cantrips that deals damage, eldritch blast is probably the best choice. It has big damage dice, great range, and few creatures have resistance to the force damage type.
Guidance is a great all-around buff that grants +1d4 to any ability check that you or an ally makes.
Characters with darkvision won't need this, but those who don't will find light to be exceedingly helpful at night or while exploring underneath the earth.
Being able to move light objects with your mind alone might not provide a constant benefit, but when you need it mage hand is clutch.
Although this isn't quite telepathic communication, message is a good way to get an idea across to an ally without a potential foe being able to hear your plan--such as coordinating a sudden betrayal.
Illusions are a little dependent on DM fiat, but if your DM is open to creativity Minor Illusion opens up some cunning options.
Spare the Dying
Cinderheim is a dangerous place, so it's inevitable that one of your allies will end up bleeding out on the desert's hot sands. Spare the dying isn't great in terms of action economy; it takes a full action to cast rather than a bonus action, and it requires you to be in touch range--but it will stabilize a party member about to shuffle off the mortal coil.
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