I think they're all near indistinguishable in combat, so we're going to have to rank them by known feats of strength, mostly from cut scenes. Things they do that few/ no one else can do.
Liara/Shep: no known unique feats. No reason to assume great strength.
Aria: Can leap multiple times what should be possible.
Samara: Able to slow her own fall. Not all that impressive, in context, but seems effortless, so likely more strength there.
Surprisingly, Ryder: can fly around using biotics to a greater degree than Samara.
Jack: defeated three YMIR mechs at once, singlehandedly, having woken from cryostasis seconds before.
No contest. Win for subject zero