Zardnaar
Legend
Clerics. There is almost no danger of permanently ruining it for a noob player because you can change spells every long rest and there is not the feature flood of warlock. Clerics also having better hit dice and proficiencies make them a bit more survivable than wizards.
I never understood why so many answer warlock to this question. I had 2 noobs at my games play Warlock and they had a horrible time. You need to really understand the system to play a warlock efficiently and its quiet easy to ruin your build by choosing wrong class feats. Also the limited spell splots are frustrating to new players who wanted to play a spellcaster to go buckwild with their spells and not to cast "Eldritch Blast" 95% of the time. Warlock also have more "difficult" demands to roleplaying due to the whole patron pact stuff, but my players liked this part of the class. Nowadays I always treat Warlock as an advanced spell caster class and advice newbies to take cleric or wizard.
At least your newbies picked Eldritch Blast.