Aeron is great , but he works more with nearby allies , and he regenerates health over 3 turns so it can be despelled by Sonya or caed … etc , and the immune to status ailments is also only for nearby allies witch make him useless in the wings ,but kunchen works with all allies and recovers a bunch of health (42 % * 1300 HP =546 HP , with 1300 HP being the average health for most 5* ) , and the defense down is also useful , along with the defense up for dark Allies from elemental link , so it’s very efficient to stack him with dark Allies , and he got more defense and more health than Aeron ( becse you want your healer to stay alive to be able to heal his allies ) , looking at the info presented here I’m leaning towards kunchen .
Consider that, IF he’s one of the featured past HOTM, your odds of getting him are lower than 1%; and if he’s not one of the featured heroes in Atlantis, the odds are negligible.