November 9, 2014 1:39 AM EST
Lorkhan was, if you believe the Mythic Dawn.
Jyggalag might have been, but nobody's heard from him in 200 years.
Sheogorath used to be Jyggalag before the Champion of Cyrodiil came along. He's also referred to as a "Sithis-shaped hole," meaning he would have power directly from Padomay.
Meridia was, or still is, a Magna Ge. Although we don't know how powerful the Magna Ge are, she is suspected to have strong connections to other Aedric gods.
After the Oblivion Crisis many would assume Mehrunes Dagon to be the most powerful, but I've heard he may just be Hermaeus Mora's pawn.
Azura can see the future, which makes her powerful in a less combat-oriented sense.
Hermaeus Mora may not be the strongest of the Princes per say, but it's pretty safe to assume he's got his tentacles in more pies than we even know exist.
If a single Daedric Prince grew powerful enough to threaten the others, they'd either rule the known universe or get killed or warped like Jyggalag by the other Princes. Old Hermaeus is the only Prince with both the subtlety and motivation to successfully rule the others.