I must say I find your post the most to my liking and a very close resemblance to what I would have chosen.Strenght - wise? Nagato is stronger than Madara. That has been almsotconfirmed by Madara himself. If he had been more powerful than Nagato, he would've acomplished his goal by himself and he wouldn't need any tailed beasts.
1. Nagato/Madara
2. Madara/Nagato
3. Itachi
4. Kisame
5. Kakuzu/Sasori
6. Deidara
7. Hidan
My list however would consist of :
1. Nagato/Madara (The deadly due! Madara needs to put more to the plate before I can really give him the number one spot, but I do consider him to be one of THEE last badies, so It must account for something)
3. Itachi (Like the previous dudes said its Itachi, even in death he still have an influence on the ninja world
4. Kisame (The only reason he is above any of these below is because hes still alive - . - )
5. Sasori (Utterly protected against any poison and have a lot of secrets up his sleeve)
6. Deidara/Orochimaru (Very tight fit between these ladies)
8. Kakuzu (Nice to have 4 hearts, to sad he didnt have 4 brains)
9. Konan (She didnt feature that much yet, but I do think her intellect allows her to surpass Hidan)
10. Hidan (It doesnt matter if your immortal, stupidity counters any ability he could have had)