Ele shaman is performing better. You don't HAVE to have Fireheart for the deck, she's useful in clutch but her played winrate is low as hell, like 5-10% below anything else in the deck.
DH is only about 1% lower winrate, but not having Blackthorn hurts a lot more than not having Fireheart.
However, Deathrattle DH was one of the battle ready decks and Ele shaman was not, so it's more likely that they'd hit shaman. I don't think either of them are oppressive enough to be nerfed right now though.
you should be able to hit at least diamond 5 or something with elemental shaman with just the Lilypad Lurkers. At that point you could decide if you wanna commit to Fireheart and go for legend. If you’re already at a high rank or Legend i would still refrain from crafting dearhrattle DH legendaries as they are kind of useless outside of the archetype. It’s hard to find any other use for cards like Al’ar in any other deck.
Given how powerful (a) card draw and (b) scaling one-drops are, I expect all Shaman decks over the next 1.5 years to be built around Nature Spells (to take full advantage of Primal Dungeoneer) and a small or large elemental package that includes Wailing Vapor and Cagematch Custodian to tutor some weapon. So you really can't go wrong with Elemental Shaman right now.
As for Deathrattle Demon Hunter, the deck got some good stuff and is strong right now, but a new expansion can easily change that and see DH move towards other builds (aggro, soul, weapon, OTK with Il'Gynoth, outcast, big demon - whatever gets some good support)
Frankly I wouldn't run any of the 3 in Deathrattle DH. Al'ar is in the deck only because of the elemental tag (which means you get him back from N'Zoth), but he is too slow and greedy. At 5-mana he has no immediate impact on the board when played (no rush, taunt or battlecry), dies to pretty much any 1-mana spell out there and then the 0/3 can be cleanly traded by anything. Also when you drop N'Zoth you mostly care about getting some rush and taunt minions to stabilise, as well as the 8/8 to push some more face damage, Al'ar would once again be just some stats with no immediate impact. As for Vectus, similar: at 5-mana with no immediate impact when played he is a bit too slow (and too greedy), and the deathrattles are random, could be good (cheat out a 4-cost deathrattle minion), or could be low impact like 'add a 4/3 murloc with rush to your hand' and 'heal your hero for 4' Finally, I was running Kurtrus in my deck before the mini-set, but he was one of the cards I cut to add the new deathrattle 3-drops. While a great card for board control when outcast, with the deck running many expensive cards it is often very hard/impossible to outcast which makes Kurtrus a much better 'discover by' card off Illidari Studies, rather than hard running it