There is a list that has been in the news recently -- a breakdown of each character's screen time in Infinity War (
imdb):
Thanos <29>
Gamora <19:30>
Tony Stark / Iron Man <18>
Thor <14:30>
Dr. Stephen Strange <11:30>
Peter Quill / Star-Lord <10:15>
Vision <9:45>
Wanda Maximoff / Scarlet Witch <9>
Dr. Bruce Banner / The Hulk <8:45>
Peter Parker / Spider-Man <7:30>
Steve Rogers <6:45>
Rocket <6>
Natasha Romanoff / Black Widow <5>
Drax <4:45>
Mantis <4:45>
Ebony Maw <4>
Proxima Midnight <3:45>
Cull Obsidian <3:45>
Corvus Glaive <3:30>
King T'Challa / Black Panther <3:30>
Groot II <3:15>
Nebula <3:15>
Okoye <3:15>
Loki <3:15>
Col. James "Rhodey" Rhodes / War Machine <3>
Eitri <2:45>
Wong <2:45>
Sam Wilson / Falcon <2:15>
James "Bucky" Barnes / White Wolf <2>
Pepper Potts <1:30>
The Stonekeeper <1:30>
Princess Shuri <1>
M'Baku <1>
Secretary Thaddeus Ross <1>
Nick Fury <1>
Maria Hill <:45>
Heimdall <:45>
Taneleer Tivan / The Collector <:45>
Ned Leeds <:15>
It touches on a point we discussed before the board reset -- how central Gamora was to the story. Thanos and the Infinity Stones are part of Gamora's background, and it was great to see the studio choose to go with the character that was dramatically appropriate rather than a character who was more popular. After all, it isn't hard to think of counter examples from other studios -- a Kitty Pride story that now is centered on Wolverine, or a Superman sequel that is all about Batman.