Including all characters who could be before Double MS Obito.
Kagyua, Hagoromo Ootsutsuki, Hagoromo's brother, Ten tails Host Madara, (Ten tails host Obito but I don't include two version of Obito), Senjutsu of six paths Naruto, Sharinnegan Sasuke.
IMO Double MS Obito with Senjuu DNA implanted would be #7th(or 8th if you include 8th Gate Gai) the strongest character along with SM Hashirama.
Double MS Obito without Senjuu DNA implanted would be #8th(or 9th if you include 8th Gate Gai ) the strongest character along with EMS Madara after SM Hashirama.
Honorably mentions of various versions of same characters being above double MS Obito: SM Double Rinnegan Madara, SM one-eyed Rinnegan Madara, Double Rinnegan Madara, One-eyed Rinnegan Madara(debatable), BSM Naruto(debetable), EMS Sasuke with curse seal(debatable), everyone else loose.
Answer: Imo Double MS Obito would be in top 10 of the strongest characters at 7th or 8th place... unless you put Indra and Ashura too..., then he would be either 9th or 10th
Top 10 list excluding ET, featless characters, or characters with no feat presented
1. Ten tails Double Rinnegan Madara
2. Naruto/Sasuke
3. SM Hashirama/Double MS Obito with Senjuu DNA
4. Heatlhy Nagato
5. Sage Kabuto/Double MS Obito without Senjuu DNA
6. SM Minato
7. Itachi
8. Tobirama/Hiruzen
9. Onooki/Muu
10. Gai
something like that