Tobi is not the same Tobi that was in Akatsuki. He has grown in power and strength since the death of both Itachi and Nagato. Tobi would obviously on top if we look at the current Tobi.
List from when all Akatsuki members were alive.
1. Itachi
2. Nagato
3. Tobi
4. Kisame
5. Sasori
6. Kakuzu
7. Konan
8. Deidara
9. Zetsu
10. Hidan
I know a lot of people like to dismiss the fact that Itachi was very powerful in the beginning of part 2. People just put Nagato on the top because he has a large flashy jutsu (Chibaku Tensei). Itachi found its weakness in part 2 and the weakness of Rinnegan. Please note that Naruto confirmed the Edo Nagato was more powerful than the one he fought in Konoha. Itachi blinded the 6 path vision and then sealed Nagato. Of course, Naruto and Bee helped with stopping Chibaku Tensei but they would have been sealed if Itachi had not saved them both. He was in fact stronger if not on par with Nagato. We just found out he had Izanami, I doubt Tobi knew about it.
Nagato is the 2nd strongest. It does not mean he isn't strong. The most credit I can give him is that he may be on par with Itachi.
Tobi was only known for his normal Sharingan and his Space-Time jutsu. Yes, he was behind the formation of Akatsuki but it does not mean he was the strongest. I would say he was more on par with Kisame.
Kisame was the beast of Akatsuki. As far as I'm concerned, he was the only capable wielder of Samahada. Samahada actually cried when he died. He was stronger than Bee, enough said.
Sasori was deadly. Sakura and Chiyo (note that Chiyo was extremely strong in her youth being only rivaled by Tsunade) were not able to defeat Sasori. He could have moved out of the sword's path as confirmed by Chiyo.
Kakuzu is as old as Madara. Had attempted to assassinate Hashirama but failed. He has to be killed 5 times, possesses all form of nature manipulation and ability to re-attach body parts. Unfortunately, he had to become the scapegoat to Naruto's jutsu for the plot's sake.
Konan was extremely intelligent as shown vs. Tobi. She's also very deadly with her paper techniques being able to attack from far or close at will. Her paper clones are deadly on their own as shown when she fought the Shino's clan.
Deidera was just an awesome character all around. Kishi mentioned that he would probably be the most powerful weapon in Kabuto's Edo army as he can blow himself up with C4 and then regenerate.
Zetsu, while not as strong as the rest, the Black Zetsu alone battled Mei's team. He is not meant to be a front line fighter but still has some fighting capabilities.
Hidan was the weakest of them all. He can be deadly IF he gets his opponent's blood. His downfall is the fact that he has to actually get the blood, drink it and get back in his circle which basically is enough time for his opponent to kill him
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I <3 Akatsuki, probably the best group of top class criminals in any show.
