I will go from low class to high class taking into account the levels (low-middle-high) That is, if someone just entered the high class they would be a high-low class warrior, of course, physical stats, magic power and additional skills can make. someone on their own enter these, an example would be Rias she has a high-low class magic power, her power of destruction although not refined still allows her to fight beings of a similar level to hers like Riser, who is medium-high. Although her physical power levels are medium-low class.
The differences between levels are also very noticeable, a high class could face 50 middle class on their own, this if they have enough experience and know how to use their power, while a high level supreme class can face a minimum of 200 high class of higher level, but that is in theory and without taking into account special skills or techniques, the character's specializations or their combat experience.
Obviously, a supreme class that specializes in healing would not be able to beat a high class that specializes entirely in battle.
Now the power levels:
Normal humans.
Low class (Fallen Angels with one pair of wings).
Middle class (Fallen Angels with two pairs of wings)
High Class (Fallen Angels with three pairs of wings)
Ultimate Class (Fallen Angels with 4 and 5 pairs of wings, low and medium level Gods)
Satan Class (Fallen Angels with 5 and 6 pairs of wings, mid and high level Gods, daiyoukai such as Yasaka and the 5 Dragon Kings)
Transcended Class (Those who surpassed their races by going beyond them, such as super demons, higher (Hades) and supreme level gods (Shiva), monsters of legend such as Typhon and Fenrir, or the Ddraig celestial dragons themselves. Albion or those who reached level like Crom Cruach).
Ex Class (The Dragon Gods: Big Red, Ophis and Trihexa)
I relied quite a bit, if not completely, on Fanfic DxD: ReKiba for these power levels. Read the fanfic, it's great.
Now for the Top 10 (I'm just my opinion):
10. Fenrir/Thor.
9. Hades.
8. Sirzechs Lucifer/Ajuka Beelzebub
7. Typhon
6. Vishmu/Brahma/Ra/Kronos/Lugh
5. Draig/Albion/Crom Cruach.
.
3. Eolhim (He is a complete Hacker if you ask me with all that he has achieved even the highest members of this top should watch their backs, although he could vary his position with Indra but I'll leave it at that).
2. Shiva.
1. Ofis.
0. Great Red/Trihexa (To no one's surprise).
