Most played cards in Dragon:

5 Decks
Bazaar of Baghdad
20 copies - 4 average
Underground Sea
16 copies - 3.2 average
Worldgorger Dragon
16 copies - 3.2 average
Polluted Delta
15 copies - 3 average
Animate Dead
13 copies - 2.6 average
Flooded Strand
13 copies - 2.6 average
Jace, Vryn's Prodigy
12 copies - 2.4 average
Force of Will
11 copies - 2.2 average
Thoughtseize
11 copies - 2.2 average
Intuition
8 copies - 1.6 average
Dig Through Time
8 copies - 1.6 average
Containment Priest
8 copies - 1.6 average
Mental Misstep
8 copies - 1.6 average
Gitaxian Probe
7 copies - 1.4 average
Necromancy
6 copies - 1.2 average
Dance of the Dead
6 copies - 1.2 average
Hurkyl's Recall
6 copies - 1.2 average
Monastery Mentor
6 copies - 1.2 average
Tasigur, the Golden Fang
6 copies - 1.2 average
Mana Crypt
5 copies - 1 average