Most played cards in Dragon:

4 Decks
Bazaar of Baghdad
16 copies - 4 average
Worldgorger Dragon
13 copies - 3.25 average
Polluted Delta
13 copies - 3.25 average
Underground Sea
12 copies - 3 average
Jace, Vryn's Prodigy
11 copies - 2.75 average
Animate Dead
10 copies - 2.5 average
Thoughtseize
8 copies - 2 average
Collective Brutality
8 copies - 2 average
Force of Will
7 copies - 1.75 average
Misty Rainforest
7 copies - 1.75 average
Null Rod
7 copies - 1.75 average
Dance of the Dead
6 copies - 1.5 average
Abrupt Decay
6 copies - 1.5 average
Tasigur, the Golden Fang
6 copies - 1.5 average
Gitaxian Probe
5 copies - 1.25 average
Intuition
5 copies - 1.25 average
Mox Ruby
4 copies - 1 average
Nature's Claim
4 copies - 1 average
Mana Crypt
4 copies - 1 average
Flooded Strand
4 copies - 1 average