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Elspeth:
5 cost, 2white - medium white mana req
Exile target permanent - most useful single target effect in the game
Noncreature spells cost 2 more to cast - it's like telling your opponents you have a Spell Pierce and allows them to prepare for it, basically useless
Return planiswalker/creature from YOUR graveyard to the battlefield and +1 them. It's a pretty decent effect, but it only allows you to hit your own graveyard so it's pretty limited in what it can do.
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Eldest Reborn:
5 cost, 1 black - very low black mana req
Each opponent sacrifices a creature or plainswalker - incredibly useful, if you play it while an opponent only has 1 targetable card out it's basically double Dreadbore and sets up a combo with the last effect
Each opponent discards a card - hand hate is one of the most powerful effects in the game
Put target creature or plainswalker from A graveyard onto the battlefield under your control. - Targets ALL graveyards, so you can steal anything you killed with the first effect
Elspeth is just all around worse imo.