“Since they’ve fought together, they knew each other’s strengths. They also understand the hope Superman stood for, that was lost [when he died], so they feel that more than the others,”
The negative impact impact of the loss of Superman on Wonder Woman and Batman can somewhat be fathomed, as The Flash and Aquaman just arrived to the Justice League team, and they have no idea of Superman’s sacrifice to save the city of Metropolis in Doomsday.
Among the Justice League team, Bruce Wayne Batman would be the one to mourn him most due to the relationship he had with Superman from inception.
Source: US Weekly