Most played cards in Doomsday:

6 Decks
Polluted Delta
24 copies - 4 average
Brainstorm
24 copies - 4 average
Lion's Eye Diamond
24 copies - 4 average
Ponder
24 copies - 4 average
Dark Ritual
24 copies - 4 average
Sensei's Divining Top
24 copies - 4 average
Doomsday
24 copies - 4 average
Gitaxian Probe
24 copies - 4 average
Cabal Therapy
23 copies - 3.83 average
Duress
22 copies - 3.67 average
Abrupt Decay
21 copies - 3.5 average
Burning Wish
16 copies - 2.67 average
Lotus Petal
14 copies - 2.33 average
Underground Sea
12 copies - 2 average
Xantid Swarm
10 copies - 1.67 average
Bloodstained Mire
10 copies - 1.67 average
Tropical Island
8 copies - 1.33 average
Volcanic Island
8 copies - 1.33 average
Empty the Warrens
7 copies - 1.17 average
Scalding Tarn
7 copies - 1.17 average