In season 1 we have Tarrlok capture Korra and keep her locked in a metal box. Then Amon comes. When Tarrlok tries to bloodbend Amon, Amon resists. How come Tarrlok couldn't resist Amon's bloodbending?
It's shown in the flashback episode that Amon was the stronger bender among the brothers.
Episode 11: Skeletons in the closet
Tarrlok: A few years later, my father taught us to bloodbend anytime, without the need of the full moon. We practiced constantly, and I hated every minute of it. I had no stomach for manipulating helpless animals. My brother, however, seemed to revel in this newfound power. He was a prodigy, mastering my father's psychic bloodbending technique by the time he was fourteen.