though for right now the most powerful are as follows...
in descending order.
onaga, the dragon king- part god, part demon, part dragon, this guy is a total beast.. even shao kahn knew he couldn't take him down alone. strong enough to stand up to rayden and an enhanced quan chi and shang tsung giving him their collective all and not even flinching....
shinnok- once an elder god, nuff said.
shao kahn- sorceror supreme.. with black magic and a vast array of fighting ability and super strength he can contend with even elder gods.
rayden- god of thunder nuff said.
wind god -(who's name escapes me at the moment)
(current sub zero and current scorpion may actually place above this category but this is where I'm sticking them for now... they have gone through some MAJOR upgrades as of late though.)
goro- right hand man of shao kahn in his attempt to kill onaga
kintaro- younger than goro, bigger, stronger, and faster, just no where near as good a fighter... (which would be why goro trounced him.)
quan chi- emmensly powerful sorceror.
shang tsung- slightly beneath quan chi's power.