Most played cards in Dragon:

4 Decks
Bazaar of Baghdad
16 copies - 4 average
Underground Sea
13 copies - 3.25 average
Flooded Strand
13 copies - 3.25 average
Worldgorger Dragon
12 copies - 3 average
Polluted Delta
12 copies - 3 average
Force of Will
11 copies - 2.75 average
Animate Dead
11 copies - 2.75 average
Jace, Vryn's Prodigy
9 copies - 2.25 average
Thoughtseize
9 copies - 2.25 average
Containment Priest
8 copies - 2 average
Mental Misstep
8 copies - 2 average
Intuition
7 copies - 1.75 average
Dig Through Time
7 copies - 1.75 average
Monastery Mentor
6 copies - 1.5 average
Gitaxian Probe
6 copies - 1.5 average
Hurkyl's Recall
6 copies - 1.5 average
Necromancy
5 copies - 1.25 average
Tasigur, the Golden Fang
5 copies - 1.25 average
Cavern of Souls
5 copies - 1.25 average
Steel Sabotage
4 copies - 1 average