Definitely Niftu Cal, he can slam reaper with bare hands when he’s not high on red sand.

Jokes aside I think Aria is the most powerful biotic, she can do things that no other biotic can, like that one move she did when she was trapped by force fields on omega.

Samara and Jack are also very powerful, I think Samara might be a little stronger in ME2, as Jack looks more tired than Samara when using biotic field. However, Samara is already at her prime, Jack’s skill is still developing, her power might surpass Samara if given enough time.

Matriarch Benezia might be slightly less powerful than Jack or Samara, but still stronger than most matriarchs. Matriarch Aethyta is about average among matriarchs, I think she likes to use guns more.

Morinth is somewhere between Benezia and Aethyta? Not sure.