In order of how strong I think they are though the characters could easily change a place or two.
Azshara is still alive right? Probably her considering what everyone says. Her mere presence is supposed to make even great mages shake in their boots.
Medhiv if he’s still alive is considered more powerful than Khadgar, so he would definitely be in the running.
Khadgar As far as rankings go, before war within I would have said Khadgar was up there, but I have no idea how weakened he is by Xal’atath. We know he’s in a wheelchair, but how much does it affect his magic.
Jaina is an incredibly powerful frost mage, and her feats cannot be underestimated. Bfa really showed off her power level, and so it’s hard to know how she compares with the best.
Kalecgos is probably up there, though his presence on screen has been a little lackluster. Him being a dragon mage, means he most likely has a large store of mana.
There are a number of mages that are now dead that would have placed in the top positions, but I tried to stick with characters that are at least somewhat hinted at being alive.