GSA question - Which is better for Endless: Ancient Dragons, or Bone Mammoths?

Not that it matters to me at this time, because I don't have the summon for the mammoths (yet). However, if they are better than the Ancient Dragons, then I will grind for them during the event.

Also, which buffs should I use for mammoths vs dragons? I know all the ones for the dragons, having hit over floor 500 with them. Just trying to figure out which ones work for the mammoths (if they are better).