Had to be Dr Strange. He, along with Iron Man, made the most out of Thanos. As one of the few characters having the most screen time, Dr Strange is a pivotal character in this episode as his usage of the time stone set the plot for next year's Avengers 4.
"We are in the endgame", "14,000,605 and only 1 where we win"
And his sacrificial bargain with Thanos in exchange of keeping Tony Stark alive, that was EPIC.