!Among the angels, Michael is clearly the most powerful. This can be seen in the final showdown between him and Lucifer. Lucifer acknowledges that it is, at best, a longshot that he should triumph, but feels compelled to fight anyway. In earlier episodes though, to other people/angels, Lucifer would be full of bravado, probably an attempt to convince himself that he could win.
!Second to him though he might be, Lucifer is an incredible power that lays waste to many beings considered deities. And not one-on-one either, they pile on to him... and he just smites them. Furthermore, while Lucifer is clearly no match for Death (Incarnate), he does manage to trick Death with magic that enslaves him. Whether this should be considered impressive or not I leave to you the reader, after all, a junkyard owner manages to accomplish the same thing later in the series.
!Next in line would be two more angels, Raphael and Gabriel. We are never given any clues as to which is stronger than the other. But both are archangels proper, and in theory capable of killing Lucifer and/or Michael (something no ordinary angel could ever manage). It seems likely that they might manage this without their angelic blades (swords of archangels, and all that), but they are armed with the means to do so at the very least.
!Next in line I would put post-resurrection (second time) Castiel. He was somewhat lowly originally, but he is quite clearly capable of resurrecting the dead after the end of season 5. While Raphael was probably still capable of smiting him, I suspect that it might have been just a bit more difficult than it would with any other angel.
!Now, compared to demons... even the lowliest angel seems both capable of smiting them and invulnerable. Alistair (a powerful demon as far as they go) laments that he cannot kill them, only send them back to Heaven temporarily.
!Crowley seems much more powerful in seasons 6 and 7, but it is revealed that he has the help of Castiel to some degree or another, and can marshal the forces of Hell in their entirety.
!I suspect that Ruby, Lilith, and Azazel were never as powerful as Crowley is in later seasons. They knew esoteric magic and might be able to interfere with powers greater than themselves (for a few moments anyway), but they are all dead and Crowley remains.
!Meg is savvy, but does not seem particularly adept at the black magic that might make her more powerful. If you ask Crowley for the spell to bind Death, 24 hours later you have a parchment in your hands. But Meg has only ever used blood to communicate with other demons.
!No other still-living (wrong word? still-existing?) demons are even named.
!It's unclear where the Hell-forged knife comes from. Demons may have constructed it, or merely came into possession of it at some point in the past.