Midoriko definitely, she created the Skikon no Tama. The story line always emphasizes on her as the strongest Miko. Kikyo is strong but could he have done what Midoriko did, possibly not seeing as she was so easily deceived দ্বারা Naraku, and Tsukiyomi is just a filler character, so the series doesn't define her as she would have been if she was. Hitomiko on the other hand is, and I'd say she's perhaps just a step lesser than Kikyo, the same goes for Tsubaki. Kagome is supposed to be the সেকেন্ড strongest Miko in the series পরবর্তি to Midoriko. Rumiko Takahashi supposedly stated this herself but I don't know if she intended for her to be stronger than Midoriko অথবা an equal but if she possesses the power to purify and rid the world of the Shikon no Tamma then she has to be one অথবা the other.
A few further points: Kikyo is stronger than Kagome only in battle, this is because of the extensive training she endured growing up as to become a Miko, and because she obviously has a much deeper understanding of the duty of her profession. Hitomiko is the same, she is also much আরো intelligent and knowledgeable than Kagome giving her an upper edge, but again this of course is due to her extensive training. And for far as I’m concerned Tsubaki was just an idiot x3
আপনি do mean spiritual power, right? I believe that Midoriko is the strongest, seeing as she created the Jewel. পরবর্তি is Kikyo, since she was revered for her spiritual power. I think Tsukiyomi is the least strongest seeing as she was only a minor character. However, if আপনি are referring to physical strength, then Midoriko would still be strongest, পরবর্তি Tsukiyomi, and lastly Kikyo. I believe Midoriko to be the strongest since she battled for seven days (that was how long she fought, right?) before she died. I believe Tsukiyomi to be the সেকেন্ড strongest since she was supposed to be a female samurai.