I think The X-men and the Heralds can take the JLA. The Heralds might be able to do it by themselves. Almost all of them can travel at the speed of light except for like Terrax and Air-Walker. Add a combined telepathic assault by the Professor X, Emma that's designed to give Rouge enough time to touch him and It's a wrap. The bodies of thwe X-men are going to litter the battle field, but so will the bodies of the JLA.