Most played cards in U/B/R Control:

3 Decks
Damnation
12 copies - 4 average
Shriekmaw
8 copies - 2.67 average
Prismatic Lens
8 copies - 2.67 average
Underground River
8 copies - 2.67 average
Graven Cairns
7 copies - 2.33 average
Foresee
7 copies - 2.33 average
Frost Marsh
7 copies - 2.33 average
River of Tears
6 copies - 2 average
Snow-Covered Island
6 copies - 2 average
Quagnoth
6 copies - 2 average
Aeon Chronicler
6 copies - 2 average
Coalition Relic
6 copies - 2 average
Dread
5 copies - 1.67 average
Extirpate
5 copies - 1.67 average
5 copies - 1.67 average
Snow-Covered Swamp
5 copies - 1.67 average
Phyrexian Ironfoot
4 copies - 1.33 average
Urborg, Tomb of Yawgmoth
4 copies - 1.33 average
Terramorphic Expanse
4 copies - 1.33 average
Aven Riftwatcher
4 copies - 1.33 average