On the contrary... / Quite the opposite...
Strongly contradicts the previous statement. More emphatic than sin embargo. Al contrario, me gustó mucho = on the contrary, I liked it very much.
—Did it bother you? —On the contrary, I found it very useful.
It's not boring; quite the opposite, it's very entertaining.
Contrary to what I thought, it turned out to be very easy.
—Are you angry? —On the contrary, I'm happy.