[Guido]

What makes a choice good or bad?
Are those that either encourage or discourage your growth as a person walking on the hazardous path that is life?
Or those leaving within you a foreboding sense of dread and fear forcing you to reflect back upon the circumstances that either you or external factors beyond your control precipitated to reach such choice, and then you ask yourself if you only had not behaved irresponsibly, if you only had the knowledge, or if you only had stood your ground instead of running away knowing full well that you had the means?
Back then would have had made such a difference had you taken a different decision? After all said and done, once a personal tragedy strikes us whether preventable or not regret is a very human response borned from our deepest dread and guilt.

What Levi chose to do was making the choice he would most likely regret the least once contemplating and weighing all that both Armin and Erwin each individually amounted to and accomplished whether for good or bad.
Because as he explained to Floch and just as Floch chose to feel at the moment he found Erwin barely alive but in agony, the Commander delivered his fair share at leading dozens upon dozens of lives at his charge to their deaths in order to secure a fleeting but conclusive victory for humanity, and this enterprise had to culminate with his death in order to reach that goal.
For Erwin, his punishment is dying without ever learning of the secrets of the basement that store the truth left behind by Grisha Yeager.
He asked Levi to make the choice for him, and Levi chose to order his Commander to lead himself (Erwin) along with the recruits to their deaths in order to distract the Beast Titan long enough so that he (Levi) could take him down.
I'm pretty sure that had Levi forced Erwin back into their hellish world after the Commander himself fulfilled his final mission, then Levi would surely had regretted it the most.
Precisely, because in exchange to forsake his dream and ambition Erwin died along with the troops to deliver a victory against all odds with virtual zero probability of survival, while for the moment Levi failed Erwin to kill the Beast Titan.
At that moment, Levi thought to himself he had no right to force Erwin back on hell to play again the role of a devil, because Erwin in exchange wished to be delivered and freed from that role if accomplishing his selfish dream was no longer possible.

In contrast, Armin is young and a naive opting to be opened for negotiation rather than resorting to violence against his foes. His cunning intellect and powers for observation and deduction have been maturing with each experience at death's doorstep ever since the Battle at Trost.
Will Armin become more in handy and resourceful for what's in store for the future?
We can't tell but the world is full of endless possibilities, and save for death nothing else is for certain. Nevertheless, what's in the grasp of the survivors is that Armin made it back thanks to Levi acquiescing following his initial choice at not bringing back Erwin, that they successfully stolen the Colossal Titan powers at the expense of devouring Bertholdt (it came full circle starting with their betrayal to let Marco die for the sake of covering their mission and ending precisely back to the start with a helpless Bertholdt screaming for help, but his former friends just stand idly without lending a hand), and, finally, ready to uncover at last the secrets of the basement.