I would pick Felix by UD> I don't think he is stopping Starling and Starling could hurt Felix, but Felix was a great fighter and he would win a decision. If Maurice Blocker could beat Starling, who later Felix demolished in 2 rounds, then he could beat Marlon. I admit Starling was a little worn out at that point. I think it was after he moved up and fought Nunn, then moved back down. So that could not help him. I never understood why Starling didn't try 154. Sort of like the question why didn't Duran fight at 140.
I would favour Trinidad based on consistency and endurance down the stretch of the fight.Starling,while a very good counter puncher and difficult to catch clean,was a stationary fighter that didn't utilize the type of lateral movement that always give Trinidad fits. Competitive fight,though,and I see a sharp counter puncher with a solid guard like Starling causing Trinidad problems throughout.
I see Starling wearing him down and knocking him out late or copping a wide UD. Felix would come right at Marlon, allowing "Moochie" to put his brilliant counterpunching skills on display. Simply put, I feel that Starling could hit Trinidad but Trinidad has major problems hitting Starling. Marlon had more natural ability. Trinidad's only hope is to KO Starling and you have to be able to hit him clean and often with hard punches to do that. Nobody hits Starling clean and often with hard punches. His only hope, imo, is if he gets in an after the bell punch ala Molinares.