I have all the heroes you have listed for final ascension, save Margaret. All of them are parked at 3/70 even if I am sitting on 19 tonics.
Among the four, I find Gregorion to be the better hero against certain titans and events as his crit bonus will benefit you to gather better overall score. He is also good in wars, splitting your 4* and 5* heroes into two monogreen teams, each with a sniper in Lianna and Greg, assuming you employ mono.
Margaret, who has the fastest mana speed among the four, may have benefited from her recent buff, but she is too squishy to be relied upon. She has the highest attack stat but Greg’s crit bonus doubles the tile damage, which outweighs the high attack stat. I highly suggest to level your mana troop to level 23, or to level 17 but you must emblem him to +8 and opt for the +2% mana bonus to support him in raids and in wars, even against titans. Doing so, you will fire his skill almost at the same time with your fast heroes
Atomos also benefited from his recent buff, changing him from a slow hero to an average one. He shines well if you have his special fire after Evelyn and Frigg as it will cause massive havoc against the enemy teams in raids and in wars.
Zocc would have been great if he was fast hero. The problem is, his mana increase/mindless attack to the target may backfire on him since it can be negated by clerics (and even by monks, I am not so sure). I find my double Hansels worth the hero slots in my primary monogreen team, accompanied by Alberich, Evelyn and Lianna.
In short, if it cannot be helped, go ascend your Greg.