2. The Flash
The Flash seems like a good choice to be the one to die. Hes iconic everyone recognises that red outfit instantly and has a long history and is a big enough name to make Trinity matter enough by making it seem momentarily meaningful and big ("Trinity was the Event where The Flash died!"). It changes the dynamics of Justice League where his buddy Green Lantern might be overcome with grief and start doing crazy things, enough so that it makes the Justice League (even more) dysfunctional and lead to further inner conflict and drama. Plus it would mean the current Flash, the rather bland Barry Allen, is replaced with the spicier former Flash Wally West for the first time in the New 52. Numerous characters have held the title of the Flash from the original Jay Garrick to Barry Allen, Wally West, and Bart Allen, so fans could expect a return from Allen at some point in the future. It would be a big name falling for this Event to make it stand out while being a nod to the characters history, bringing it in to the new continuity, and give new readers a chance to experience a new version of the Flash. DC are marketing Trinity War as the first major DC Event since the New 52 began with Flashpoint, an Event instigated by the Flash. Whether this Event could also be brought about by Flash's death or culminate in it has some symmetry with the character's impact on the DCU in recent years.