I'd say a tie between Esther and Qetsiyah
People keep bringing up the Other Side as proof that Qetsiyah was more powerful but, why would Esther need to create a dimension?
She didn't want her children to die, and besides, the Other Side was already there
She created an immortal race, just like Qetsiyah
She created a cure (the spell she intended to use)
She's heralded as one of the most powerful witches in history
It seems to me that power wise, they have the same reputation
Actually,there are a few differences power-wise between them.
Esther didn't create an immortal race.She only copied a spell and due to not being as powerful as Qetsiyah didn't manage to make her children fully immortal.They were still very much killable while the immortality Qetsiyah created was truly perfect in every aspect.
Also,the very fact that Esther had to use dark magic for extra power to perform the spell while Qetsiyah only drew on natural power says much about the power of the two.
And lastly,Esther could only perform the curing spell while simultaneously channeling the entire Bennett bloodline(including Qetsiyah) AND the full moon.Once Abby died,she lost all of that power.It wasn't hers,while Qetsiyah required no bloodlines or special times to do it,presumingly.
Then again,both of them made all of this in different interests. Qetsiyah wanted eternity while Esther wanted speed and strength.
Also,during Qetsiyah's time,there were no spirits to create consequences on her immortality spell,while in the 10th century,the spirits were very much ready to limit Esther's spell in as many ways as possible.
Esther modified the spell so her children could be faster and stronger than werewolves. There is nothing that says she couldn't do the exact same spell. Also it wasn't spirits that created consequences, it was nature. The consequence for creating a true immortal is doppelgangers. Esther's consequence was for every strength there was a weakness. Immortals have no strengths over humans. Silas physic abilities could be obtained by any human who lived 2000 years. theoretically.
Immortal are not better than Originals vampires. Amara was carted around by travelers for two thousands years suffering. Silas was locked away for two thousand years. A physically stronger human can get the best of an Immortal. Tie them up and go drop them in the ocean. Superior? I don't think so.
A lot of things witches do are impressive. It doesn't mean another witch couldn't do the same things. Better in some cases. The greatest feats witches have done, simply should not have been done.
Obviously Esther couldn't repeat the same spell, otherwise she would have simply added the physical factors on to Qetsiyah's spell, not changed it completely. Esther had to change the spell, change the ingredients for what she could do with her power. Look at how Qetsiyah and Esther actually granted Immortality. Qetsiyah didn't have to draw or channel anything to grant Immortality, yet Esther needed the White Oak Tree. The Tree had nothing to do with giving Esther's children superior physical abilities, so tell me, why would she need to channel the White Oak Tree if she could perform the same spell...? The only logical conclusion is that she wasn't as powerful.
The only consequence for creating a truly Immortal being is Dopplegangers, that's correct, and that is because it's the ONLY consequence that Nature is able to give. Even then, it's not a weakness to a truly Immortal being because hell, even when a Witch links a Immortal to their Doppleganger, they're still Immortal. The Originals have a handfull of weaknesses that can be used against them, and they can be killed, permenantly.
Actually Immortals do have strength over Humans. Jeremy was a Hunter, clearly stronger than your average Human, probably stronger than most actually, and he was still overpowered by Silas, at least momentarily. The only reason Jeremy gained the upper hand was because he was a better fighter.
Anyway, what species you think is "better" is irrelevant. Nature only cares about one thing, not allowing Immortal beings to exist. Silas was truly Immortal, the Originals are not. That alone makes Immortals superior to Originals, at least in Nature's eyes, (if it has eyes of course).
We could also ask why didn't Qetsiyah enhance strength and speed? It could have easily have been her being carted around for two thousand years instead of Amara. Being immortal turned out to be a curse more than a gift for both Silas and Amara. Being truly immortal may be the bigger offense by nature, but I am not sure that makes them superior. Considering the originals only had to burn down one tree to eliminate their one true weakness. Albeit they missed a sapling, lol
I rank Qetsiyah #1 for the ability to desiccate Silas. Bonnie and Abby had to stop a heart to do this spell. She did this without incantation or channeling power. This example is not skewed by extra power sources. This was pure Qetsiyah and nothing else. Her ability to link Stefan and Silas puts her above an entire group of travelers.
I rank Esther #2 based on comparable accomplishments to Qetsiyah. Her skill is comparable because she was able to counter problems as easily as Qetsiyah. Qetsiyah countered immortality with The Cure. Esther created daylight rings, moonlight rings and a way to eliminate all vampires in one swoop.
I rank Silas no where. Silas did not show any skill as a witch. Everything about Silas is assumption. His page is filled with fluff, basic witch stuff. They implied he was powerful, just never showed it.
I rank Bonnie as the average Bennet witch. Being a Bennett witch ranks her higher than most witches. All the things she has done could have been accomplished by any Bennett witch. Expression and mixing magic could have been done by any Bennett witch. Except an informed Bennett witch would not do those things. They would not be consumed by expression or try mixing magic causes ones death. Bennett Line up in order: Qetsiyah, Ayana, Emily, Witch of the five, Bonnie. Being reckless doesn't make you powerful.
I rank Davina as the average Harvest witch. There has been no witch with more raw power than broken Harvest Davina. Like Bonnie being a Harvest witch ranks her highest than most witches. In the end she was as reckless as Bonnie and almost destroyed a city.